[Doc] Document budget_policy_id in databricks_app resource and data sources (#4557)

## Changes
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## Tests
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- [x] relevant change in `docs/` folder

Author: alexott

NEXT_CHANGELOG.md

@@ -9,6 +9,7 @@
 ### Documentation
 
  * Document management of permissions of `databricks_budget_policy` resource ([#4561](https://github.com/databricks/terraform-provider-databricks/pull/4561))
+ * Document `budget_policy_id` in `databricks_app` resource and data sources ([#4557](https://github.com/databricks/terraform-provider-databricks/pull/4557))
 
 ### Exporter
 

docs/data-sources/app.md

@@ -45,6 +45,8 @@ In addition to all arguments above, the following attributes are exported:
   * `service_principal_id` - id of the app service principal
   * `service_principal_name` - name of the app service principal
   * `default_source_code_path` - The default workspace file system path of the source code from which app deployment are created. This field tracks the workspace source code path of the last active deployment.
+  * `budget_policy_id` - The Budget Policy ID set for this resource.
+  * `effective_budget_policy_id` - The effective budget policy ID.
 
 ### resources Attribute
 

docs/data-sources/apps.md

@@ -37,6 +37,8 @@ The following attributes are exported:
   * `service_principal_id` - id of the app service principal
   * `service_principal_name` - name of the app service principal
   * `default_source_code_path` - The default workspace file system path of the source code from which app deployment are created. This field tracks the workspace source code path of the last active deployment.
+  * `budget_policy_id` - The Budget Policy ID set for this resource.
+  * `effective_budget_policy_id` - The effective budget policy ID.
 
 ### resources Attribute
 

docs/resources/app.md

@@ -44,6 +44,7 @@ The following arguments are required:
 
 * `name` - (Required) The name of the app. The name must contain only lowercase alphanumeric characters and hyphens. It must be unique within the workspace.
 * `description` - (Optional) The description of the app.
+* `budget_policy_id` - The optional Budget Policy ID set for this resource.
 * `resources` - (Optional) A list of resources that the app have access to.
 
 ### resources Configuration Attribute
@@ -87,6 +88,7 @@ In addition to all arguments above, the following attributes are exported:
 * `service_principal_id` - id of the app service principal
 * `service_principal_name` - name of the app service principal
 * `default_source_code_path` - The default workspace file system path of the source code from which app deployment are created. This field tracks the workspace source code path of the last active deployment.
+* `effective_budget_policy_id` - The effective budget policy ID.
 
 ## Import