feat: add sample for grpc startup probe

[glasnt]

Description

Fixes b/315103435

This sample is untestable using the hello container, because it does not implement grpc healthchecks. (The grpc liveness probe sample does not override the startup probe, so it successfully deploys. Since this is a startup probe, the deployment will fail, so it is untestable using the default image.)

Note: If you are not associated with Google, open an issue for discussion before submitting a pull request.

Checklist

Readiness

• Yes, merge this PR after it is approved
• No, don't merge this PR after it is approved

Style

• My sample follows the rules described for Terraform in the Effective Samples style guide
• My sample follows the other requirements and best practices in the Contributing
  guide

Testing

• I have performed tests described in the Contributing guide:

  • Tests pass: terraform apply
  • Lint pass: terraform fmt check

Intended location

• Yes, this sample will be (or already is) included on cloud.google.com
  Location(s): https://cloud.google.com/run/docs/configuring/healthchecks#grpc-startup-probe

[snippet-bot]

Here is the summary of changes.

You are about to add 1 region tag.

• run/healthchecks_startup_probe_grpc/main.tf:24, tag cloudrun_healthchecks_startup_probe_gRPC

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[msampathkumar]

LGTM.

[glasnt]

/gcbrun