Add fields related to health checked targets to dns_record_set resource

[modular-magician]

This resource used to support two types of routing policies: weighted round robin (wrr) and geo location (geo). Now we will be supporting a third option: primary-backup.

In addition, the existing routing types are being updated in two ways:

• enabled_geo_fencing is being added to support fencing behavior of all geo items
• health_checked_targets is being added to both wrr and geo, which provides another option for configuring the routing behavior

All together, this work aims to support health checking capabilities for internal load balancers.

b/239887327

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).
• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

dns: added `primary_backup` to `routing_policy` block of `google_dns_record_set` resource

dns: added `enable_geo_fencing` to `routing_policy` block of `google_dns_record_set` resource

dns: added `health_checked_targets` to `wrr` and `geo` blocks of `google_dns_record_set` resource

Derived from GoogleCloudPlatform/magic-modules#6665