Add support for policy_name field in Placement Policy

[modular-magician]

Custom Placement Policy is a GKE node pool feature that allows users to use a custom resource placement policy.

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).
• 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).
• Generated Terraform providers, and ran make test and make lint in the generated providers to ensure it passes unit and linter tests.
• Ran relevant acceptance tests using my own Google Cloud project and credentials (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know).
• Read Write release notes before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

container: added `placement_policy.policy_name` field to `google_container_node_pool` resource

Note: I've run the added acceptance tests successfully, but the make testacc TEST=./google TESTARGS='-run=TestAccContainerNodePool' is partially failing. I'm running into some issues related to my project, e.g. INVALID_ARGUMENT: disabling pod cidr overprovision is not allowed for this project or Error: Error waiting for creating GKE cluster: The network "default" does not have available private IP space in 10.0.0.0/8 to reserve a /14 block for containers for cluster....

Derived from GoogleCloudPlatform/magic-modules#8475

[github-actions]

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