Add PubSub action to DLP Job Trigger

[modular-magician]

Adds support for an additional type of action, "Publish to PubSub", to the Data Loss Prevention Job Trigger schema.

This allows terraform users to configure their DLP triggers to publish to a PubSub topic upon completion.

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. both of those failed with make: *** No rule to make target 'test' (or 'lint'). Stop.
• 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). I could not find the section "tests" in the linked document.
• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

dlp: added pubsub action to `google_data_loss_prevention_job_trigger`

Derived from GoogleCloudPlatform/magic-modules#6757