Add delete support and handwriten sweeper for Firebase Web App

[modular-magician]

Support DELETE for Firebase Web apps. By default the delete is soft with a 30 days expiration. For the sweeper, there is no point keeping test apps for 30 days thus the hard-delete.

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Release Note Template for Downstream PRs (will be copied)

firebase: added deletion support and new field `deletion_policy` for `google_firebase_web_app`

Derived from GoogleCloudPlatform/magic-modules#6652