Adds enterprise_config_resource_name field to cloudbuild trigger resource in order to support github enter…

[modular-magician]

…prise triggers

Resolves #9956

Adds github enterprise trigger support to cloud build triggers by adding github.enterprise_config_resource_name field.

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• 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).
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• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

cloudbuild: added `github.enterprise_config_resource_name` field to `google_cloudbuild_trigger` resource

Derived from GoogleCloudPlatform/magic-modules#7236

[kuba-vodafone]

anyone knows when this change will be included in the release?

[github-actions]

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