Adding support for week5 maintenance update track

[modular-magician]

Adding support for week5 update track in the maintenance settings to provide longer advance notification

The primary objective of 40 day notification/week5 is to provide Cloud SQL users with greater flexibility and control over scheduling maintenance to minimize its impact on their businesses. Cloud SQL plans to offer a new order of update option that guarantees customers a minimum of 35 days advance notice. Users will receive notification between 35-42 days in advance of their maintenance event, depending on when their maintenance window is compared to the date that the maintenance rollout began.

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

[x] 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).
[x] Generated Terraform, and ran make test and make lint to ensure it passes unit and linter tests.
[x] 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).
[x] Ran relevant acceptance tests (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know).

Release Note Template for Downstream PRs (will be copied) -

sql: a new value `week5` is now supported for `setting.maintenance_window.update_track` in `google_sql_database_instance` resource

Derived from GoogleCloudPlatform/magic-modules#10732