Public IP Support for AlloyDB

[modular-magician]

Description:
Add support to enable public IP on an AlloyDB instance, and set a list of authorized external networks that are able to connect to the public IP of the instance. This PR has some custom code to allow instances to be created with public IP enabled as the API currently prohibits it. I plan on removing this custom code in a future PR once the API is updated, but this shouldn't be a breaking change.

This is for beta and GA terraform support.

Issue:

• b/301272397
• Fixes AlloyDB public IP assignment in beta provider #17091

Release Note Template for Downstream PRs (will be copied)

alloydb: added `network_config` field to `google_alloydb_instance` resource

alloydb: added `public_ip_address` field  to `google_alloydb_instance` resource

Derived from GoogleCloudPlatform/magic-modules#10331

[github-actions]

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