Added pubsubConfig and webhookConfig support to the cloud build resource.

[modular-magician]

Google have API documentation to create a pub/sub and webhook trigger in the cloud build resource, but, the terraform google provider doesn't. I have updated the terraform resource to add that support.

Fixes hashicorp/terraform-provider-google#8692, hashicorp/terraform-provider-google#9189

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

cloudbuild: Added `pubsub_config` and `webhook_config` parameter to `google_cloudbuild_trigger`.

Derived from GoogleCloudPlatform/magic-modules#4931

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