[Doc] Added budget_policy resource and data source documentation (#4543)

## Changes
<!-- Summary of your changes that are easy to understand -->
Budget policy resource is being added through terraform autogeneration,
this PR adds the documentation for this resource until it's generated.
Added documentation for:
- databricks_budget_policy resource
- databricks_budget_policy data source
- databricks_budget_policies data source

## Tests
<!-- 
How is this tested? Please see the checklist below and also describe any
other relevant tests
-->
N/A
- [ ] `make test` run locally
- [x] relevant change in `docs/` folder
- [ ] covered with integration tests in `internal/acceptance`
- [ ] using Go SDK
- [ ] using TF Plugin Framework

Author: tanmay-db

NEXT_CHANGELOG.md

@@ -8,6 +8,8 @@
 
 ### Documentation
 
+* Added budget_policy resource and data source documentation
+
 ### Exporter
 
 ### Internal Changes

docs/data-sources/budget_policies.md

@@ -0,0 +1,29 @@
+---
+subcategory: "FinOps"
+---
+# databricks_budget_policies Data Source
+This data source can be used to fetch the list of budget policies. 
+
+-> **Note** This data source can only be used with an account-level provider!
+
+
+## Example Usage
+
+Getting a list of all budget policies:
+
+```hcl
+data "databricks_budget_policies" "all" {
+}
+```
+
+## Argument Reference
+- `filter_by` - A filter to apply to the list of policies. This consists of: 
+    - `policy_name` - The partial name of policies to be filtered on. If unspecified, all policies will be returned.
+    - `creator_user_id` - The policy creator user id to be filtered on. If unspecified, all policies will be returned.
+    - `creator_user_name` - The policy creator user name to be filtered on. If unspecified, all policies will be returned.
+
+## Attribute Reference
+
+Data source exposes the following attributes:
+
+- `budget_policies` - The list of budget policy.

docs/data-sources/budget_policy.md

@@ -0,0 +1,30 @@
+---
+subcategory: "FinOps"
+---
+# databricks_budget_policy Data Source
+This data source can be used to get a single budget policy. 
+
+-> **Note** This data source can only be used with an account-level provider!
+
+## Example Usage
+
+Referring to a budget policy by id:
+
+```hcl
+data "databricks_budget_policy" "this" {
+  policy_id = "test"
+}
+```
+
+## Argument Reference
+
+Data source allows you to get a budget policy by the following attribute
+
+- `policy_id` - ID of the budget policy.
+
+## Attribute Reference
+
+Data source exposes the following attributes:
+
+- `policy_id` - The id of the budget policy.
+- `policy_name` - The name of the budget policy.

docs/resources/budget_policy.md

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+---
+subcategory: "FinOps"
+---
+# databricks_budget_policy Resource
+
+Administrators can use budget policies to ensure that the correct tags appear automatically on serverless resources without depending on users to attach tags manually, allowing for customized cost reporting and chargebacks. Budget policies consist of tags that are applied to any serverless compute activity incurred by a user assigned to the policy. The tags are logged in your billing records, allowing you to attribute serverless usage to specific budgets.
+
+-> **Note** This resource can only be used with an account-level provider!
+
+
+## Example Usage
+
+```hcl
+resource "databricks_budget_policy" "this" {
+  policy_name = "my-budget-policy"
+  custom_tags = [{
+    key = "mykey"
+    value = "myvalue"
+  }]
+}
+```
+
+## Argument Reference
+
+The following arguments are available:
+* `policy_name` - (Required) The name of the policy. Must be unique among active policies. Can contain only characters from the ISO 8859-1 (latin1) set.
+* `custom_tags` - (Optional) A list of tags defined by the customer. At most 20 entries are allowed per policy. 
+
+### custom_tags Configuration Block
+* `key` - The key of the tag. - Must be unique among all custom tags of the same policy. Cannot be “budget-policy-name”, “budget-policy-id” or "budget-policy-resolution-result" as these tags are preserved. 
+* `value` - The value of the tag. 
+
+
+## Attribute Reference
+
+In addition to all arguments above, the following attribute is exported:
+* `policy_id` - ID of the budget policy 
+
+
+## Import
+
+This resource can be imported by ID.
+
+```sh
+terraform import databricks_budget_policy.this policy_id
+```