Add support for parameter manager parameter datasource google_parameter_manager_parameter (#12639) (#20953)

[upstream:2fe120888b7bca28fabf618c9bb3432afeb50f6a]

Signed-off-by: Modular Magician <[email protected]>

Author: modular-magician

.changelog/12639.txt

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+```release-note:new-datasource
+`google_parameter_manager_parameter`
+```

google/services/parametermanager/data_source_parameter_manager_parameter.go

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+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: MPL-2.0
+package parametermanager

google/services/parametermanager/data_source_parameter_manager_parameter_test.go

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+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: MPL-2.0
+package parametermanager_test

website/docs/d/parameter_manager_parameter.html.markdown

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+---
+subcategory: "Parameter Manager"
+description: |-
+  Get information about a Parameter Manager Parameter.
+---
+
+# google_parameter_manager_parameter
+
+Use this data source to get information about a Parameter Manager Parameter.
+
+~> **Warning:** This datasource is in beta, and should be used with the terraform-provider-google-beta provider.
+See [Provider Versions](https://terraform.io/docs/providers/google/guides/provider_versions.html) for more details on beta datasources.
+
+## Example Usage 
+
+```hcl
+data "google_parameter_manager_parameter" "parameter_datasource" {
+  parameter_id = "foobar"
+}
+```
+
+## Argument Reference
+
+The following arguments are supported:
+
+* `parameter_id` - (required) The name of the parameter.
+
+* `project` - (optional) The ID of the project in which the resource belongs.
+
+## Attributes Reference
+See [google_parameter_manager_parameter](https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/parameter_manager_parameter) resource for details of all the available attributes.