feat(all): auto-regenerate gapics (#3587)

This is an auto-generated regeneration of the gapic clients by
cloud.google.com/go/internal/gapicgen. Once the corresponding genproto PR is
submitted, genbot will update this PR with a newer dependency to the newer
version of genproto and assign reviewers to this PR.

If you have been assigned to review this PR, please:

- Ensure that the version of genproto in go.mod has been updated.
- Ensure that CI is passing. If it's failing, it requires your manual attention.
- Approve and submit this PR if you believe it's ready to ship.


Corresponding genproto PR: googleapis/go-genproto#519

Changes:

feat(dialogflow/cx): added support for test cases and agent validation
  PiperOrigin-RevId: 352834280
  Source-Link: googleapis/googleapis@f83715b

docs(retail): Put resource paths in code spans and use absolute URLs
  PiperOrigin-RevId: 352807727
  Source-Link: googleapis/googleapis@dc9821e