feat: Add Neon PostgreSQL preview API commands with parameter mapping fixes

- Added 13 new commands for Neon PostgreSQL 2025-06-23-preview API
- Fixed critical parameter mapping issues in endpoint/database/role create commands
- Added comprehensive test suite with 6 test methods covering all functionality
- Updated azext_metadata.json with new command registrations

New Commands Added:
- az neon postgres endpoint create/list/delete
- az neon postgres neon-database create/list/delete
- az neon postgres neon-role create/list/delete
- az neon postgres get-postgres-version

Parameter Mapping Fixes:
- Fixed URL parameter mapping to use project_id/branch_id when available
- Resolved 'branch not found' errors in create commands
- Ensured proper API endpoint construction for nested resources

Testing:
- All 6 tests passing (100% success rate)
- Comprehensive validation of parameter mapping fixes
- Help command testing for all new commands
- Parameter validation testing for required fields

Author: Bhargavsaichinni

src/neon/azext_neon/aaz/latest/neon/postgres/__init__.py

@@ -10,3 +10,4 @@
 
 from .__cmd_group import *
 from ._create import *
+from ._get_postgres_version import *

src/neon/azext_neon/aaz/latest/neon/postgres/_get_postgres_version.py

@@ -0,0 +1,183 @@
+# --------------------------------------------------------------------------------------------
+# Copyright (c) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT License. See License.txt in the project root for license information.
+#
+# Code generated by aaz-dev-tools
+# --------------------------------------------------------------------------------------------
+
+# pylint: skip-file
+# flake8: noqa
+
+from azure.cli.core.aaz import *
+
+
+@register_command(
+    "neon postgres get-postgres-version",
+)
+class GetPostgresVersion(AAZCommand):
+    """Action to retrieve the PostgreSQL versions.
+    """
+
+    _aaz_info = {
+        "version": "2025-06-23-preview",
+        "resources": [
+            ["mgmt-plane", "/subscriptions/{}/resourcegroups/{}/providers/neon.postgres/getpostgresversions", "2025-06-23-preview"],
+        ]
+    }
+
+    def _handler(self, command_args):
+        super()._handler(command_args)
+        self._execute_operations()
+        return self._output()
+
+    _args_schema = None
+
+    @classmethod
+    def _build_arguments_schema(cls, *args, **kwargs):
+        if cls._args_schema is not None:
+            return cls._args_schema
+        cls._args_schema = super()._build_arguments_schema(*args, **kwargs)
+
+        # define Arg Group ""
+
+        _args_schema = cls._args_schema
+        _args_schema.resource_group = AAZResourceGroupNameArg(
+            required=True,
+        )
+
+        # define Arg Group "Parameters"
+
+        _args_schema = cls._args_schema
+        _args_schema.version = AAZIntArg(
+            options=["--version"],
+            arg_group="Parameters",
+            help="The major PostgreSQL version number",
+        )
+        return cls._args_schema
+
+    def _execute_operations(self):
+        self.pre_operations()
+        self.OrganizationsGetPostgresVersions(ctx=self.ctx)()
+        self.post_operations()
+
+    @register_callback
+    def pre_operations(self):
+        pass
+
+    @register_callback
+    def post_operations(self):
+        pass
+
+    def _output(self, *args, **kwargs):
+        result = self.deserialize_output(self.ctx.vars.instance, client_flatten=True)
+        return result
+
+    class OrganizationsGetPostgresVersions(AAZHttpOperation):
+        CLIENT_TYPE = "MgmtClient"
+
+        def __call__(self, *args, **kwargs):
+            request = self.make_request()
+            session = self.client.send_request(request=request, stream=False, **kwargs)
+            if session.http_response.status_code in [200]:
+                return self.on_200(session)
+
+            return self.on_error(session.http_response)
+
+        @property
+        def url(self):
+            return self.client.format_url(
+                "/subscriptions/{subscriptionId}/resourceGroups/{resourceGroupName}/providers/Neon.Postgres/getPostgresVersions",
+                **self.url_parameters
+            )
+
+        @property
+        def method(self):
+            return "POST"
+
+        @property
+        def error_format(self):
+            return "MgmtErrorFormat"
+
+        @property
+        def url_parameters(self):
+            parameters = {
+                **self.serialize_url_param(
+                    "resourceGroupName", self.ctx.args.resource_group,
+                    required=True,
+                ),
+                **self.serialize_url_param(
+                    "subscriptionId", self.ctx.subscription_id,
+                    required=True,
+                ),
+            }
+            return parameters
+
+        @property
+        def query_parameters(self):
+            parameters = {
+                **self.serialize_query_param(
+                    "api-version", "2025-06-23-preview",
+                    required=True,
+                ),
+            }
+            return parameters
+
+        @property
+        def header_parameters(self):
+            parameters = {
+                **self.serialize_header_param(
+                    "Content-Type", "application/json",
+                ),
+                **self.serialize_header_param(
+                    "Accept", "application/json",
+                ),
+            }
+            return parameters
+
+        @property
+        def content(self):
+            _content_value, _builder = self.new_content_builder(
+                self.ctx.args,
+                typ=AAZObjectType,
+                typ_kwargs={"flags": {"client_flatten": True}}
+            )
+            _builder.set_prop("version", AAZIntType, ".version")
+
+            return self.serialize_content(_content_value)
+
+        def on_200(self, session):
+            data = self.deserialize_http_content(session)
+            self.ctx.set_var(
+                "instance",
+                data,
+                schema_builder=self._build_schema_on_200
+            )
+
+        _schema_on_200 = None
+
+        @classmethod
+        def _build_schema_on_200(cls):
+            if cls._schema_on_200 is not None:
+                return cls._schema_on_200
+
+            cls._schema_on_200 = AAZObjectType()
+
+            _schema_on_200 = cls._schema_on_200
+            _schema_on_200.versions = AAZListType(
+                flags={"required": True},
+            )
+
+            versions = cls._schema_on_200.versions
+            versions.Element = AAZObjectType()
+
+            _element = cls._schema_on_200.versions.Element
+            _element.version = AAZIntType()
+
+            return cls._schema_on_200
+
+
+class _GetPostgresVersionHelper:
+    """Helper class for GetPostgresVersion"""
+
+
+__all__ = ["GetPostgresVersion"]