feat(google-cloud-apigee_registry-v1)!: replace gem with tombstone

[torreypayne]

Replaces google-cloud-apigee_registry-v1 with a minimal tombstone package.

Details of Changes

• Generated via toys tombstone-library using updated templates from googleapis/ruby-common-tools#453 and googleapis/ruby-common-tools#455.
• Replaces functional code with minimal tombstone skeleton (version constant, README, LICENSE, .yardopts).
• Includes minimal Rakefile with require "bundler/gem_tasks" to ensure automated release builds (rake build) succeed out of the box during CI/CD packaging.
• Removes all runtime dependencies and functional code.
• Merging with feat!: conventional commit breaking change prefix will bump the package to its next major version: 1.0.0.

Fixes: b/545644248

[torreypayne]

Closing in favor of consolidating both gems into #36233.