ci: derive generator tool versions from modules

[jeffspahr]

Summary

• derive the grpc-gateway, protobuf, protoc-gen-go-grpc, and Argo CLI versions from their canonical Go module metadata
• track go-swagger in a dedicated Dependabot-managed tools module and remove dead or duplicated version pins
• run generated-file validation only for relevant generator changes while preserving the required check name

Why

Generator versions could drift from the modules they serve because Dependabot updated go.mod without updating arbitrary Dockerfile environment variables. This makes the module manifests the source of truth and teaches CI which grouped Go updates actually require regeneration.

Standalone release downloads such as protoc and googleapis remain explicit pins because the configured Dependabot ecosystems cannot track them reliably.

Verification

• built backend/api/Dockerfile successfully
• checked all installed generator versions in the resulting image
• regenerated the v2beta1 API and confirmed no generated-file diff
• ran all 158 CI script unit tests successfully
• ran go mod verify for the tools module
• parsed the modified workflows and checked Makefile dependency wiring
• ran git diff --check

[google-oss-prow]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[google-oss-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please ask for approval from jeffspahr. For more information see the Kubernetes Code Review Process.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• .github/OWNERS
• backend/OWNERS
• docs/OWNERS
• test/OWNERS
• third_party/OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment