java mgmt, typespec config for apicenter (Azure#39516)

* feat(apicenter): add Java emitter configuration for Api Center management

- Configure @azure-tools/typespec-java emitter with output directory
- Set service directory to sdk/apicenter
- Define namespace as com.azure.resourcemanager.apicenter
- Set service name to Api Center
- Apply azure flavor configuration

* feat(apicenter): add service-dir parameter to tspconfig.yaml

- Add parameters section with service-dir default value
- Set default service directory to "sdk/apicenter"
- Configure tspconfig.yaml for proper service generation

* refactor(apicenter): update tspconfig.yaml configuration

- Remove quotes around flavor value from "azure" to azure
- Remove unused service-dir option
- Remove unused linter configuration

* refactor(apicenter): remove unused openapi3 import

Remove unused "@typespec/openapi3" import from models.tsp
to clean up dependencies and maintain code consistency.

* feat(apicenter): add client specification with Java compatibility headers

Add ApiCenter.Management client specification file that includes
legacy Java header property names for compatibility with existing
codebase using Azure Core EtagResponseEnvelope.

Author: v-huizhu2

specification/apicenter/ApiCenter.Management/client.tsp

@@ -0,0 +1,9 @@
+import "./main.tsp";
+import "@azure-tools/typespec-client-generator-core";
+
+using Azure.ClientGenerator.Core;
+
+namespace Microsoft.ApiCenter;
+
+// Preserve legacy Java header property names for compatibility
+@@clientName(Azure.Core.EtagResponseEnvelope.etagHeader, "etag", "java");

specification/apicenter/ApiCenter.Management/models.tsp

@@ -1,7 +1,6 @@
 import "@typespec/rest";
 import "@typespec/http";
 import "@typespec/openapi";
-import "@typespec/openapi3";
 
 using TypeSpec.Rest;
 using TypeSpec.Http;

specification/apicenter/ApiCenter.Management/tspconfig.yaml

@@ -1,3 +1,6 @@
+parameters:
+  "service-dir":
+    default: "sdk/apicenter"
 emit:
   - "@azure-tools/typespec-autorest"
 options:
@@ -7,6 +10,11 @@ options:
     emit-common-types-schema: "never"
     output-file: "{azure-resource-provider-folder}/{service-name}/{version-status}/{version}/apicenter.json"
     use-read-only-status-schema: true
+  "@azure-tools/typespec-java":
+    emitter-output-dir: "{output-dir}/{service-dir}/azure-resourcemanager-apicenter"
+    namespace: "com.azure.resourcemanager.apicenter"
+    service-name: "Api Center"
+    flavor: azure
 linter:
   extends:
     - "@azure-tools/typespec-azure-rulesets/resource-manager"