Restrict project ID parameters for GAR setup scripts

What does this MR do and why?

Restrict project ID parameters for GAR setup scripts

These scripts currently allow any string parameters, but they are expecting a Google Project ID. We should restrict these parameters so that shell special characters cannot be passed into the scripts through URL parameters.

This MR does not change the wlif.sh endpoint, because it will be removed in !156699 (merged) . This MR is independent of that one, and can be merged at any time.

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Before	After

How to set up and validate locally

1. Ensure you are simulating a SaaS environment
2. curl the integrations API endpoint with an invalid project ID:

   curl "https://gdk.test:3443/api/v4/projects/8/google_cloud/setup/integrations.sh?google_cloud_artifact_registry_project_id=%5C$%5C(curl%20capybara.net%5C)&enable_google_cloud_artifact_registry=true" \
     -H 'Authorization: Bearer ADMIN_TOKEN' \
     -H 'Accept: *'

3. Verify you receive a 400 response with "error": "google_cloud_artifact_registry_project_id is invalid"
4. curl the runners API endpoint with an invalid project ID:

   curl "https://gdk.test:3443/api/v4/projects/8/google_cloud/setup/runner_deployment_project.sh?google_cloud_project_id=%5C$%5C(curl%20capybara.net%5C)" \
     -H 'Authorization: Bearer ADMIN_TOKEN' \
     -H 'Accept: *'

5. Verify you receive a 400 response with "error": "google_cloud_project_id is invalid"

Related to #457804