Add support for edge_security_policy to google_compute_backend_service

[modular-magician]

Fixes hashicorp/terraform-provider-google#12867

Adds edge_security_policy field to the backend service resource in the compute api.yaml and terraform.yaml files, adds support for the post_create update command in compute_backend_service_security_policy.go.erb, and updates the corresponding handwritten test.

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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).
• 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)

compute: add support for 'edge_security_policy' field to 'google_compute_backend_service' resource.

Derived from GoogleCloudPlatform/magic-modules#7120