adding data source for identity pool provider

[modular-magician]

final part of hashicorp/terraform-provider-google#7455
this add a datasource for google_iam_workload_identity_pool_provider similar to the datasource google_iam_workload_identity_pool that was added in #4134 This is the data source version of the resource that is added in #4129

If this PR is for Terraform, I acknowledge that I have:

• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
• Generated Terraform, and ran make test and make lint to ensure it passes unit and linter tests.
• Ensured that all new fields I added that can be set by a user appear in at least one example (for generated resources) or third_party test (for handwritten resources or update tests).
• Ran relevant acceptance tests (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know). warning running the new data source test locally fails with a 404 error. I had the same issue with the previous PR add doc for iam_member #4134 but those testa apparantly run okay at your end. I never figured out what is wrong at my end.
• Read the Release Notes Guide before writing my release note below.

Fixes hashicorp/terraform-provider-google#7455

`google_iam_workload_identity_pool_provider`

I'll keep this in draft until #4129 is merged as this branch also includes those changes. The diff will clean up to only the data source changes once that PR is merged

Derived from GoogleCloudPlatform/magic-modules#4181