Adding plugin .tar file to artifact.

[rafaelwestphal]

Description

Making so that the github hook also generate the plugin tar.
Adding the newly generated plugin .tar.gz to the build artifacts so it can be accessed during the integration tests.

Related issue

b/394644858

How has this been tested?

Manually tested and verified that the .tar.gz will appear on the correct bucket.

Checklist:

• Unit tests
  • Unit tests do not apply.
  • Unit tests have been added/modified and passed for this PR.
• Integration tests
  • Integration tests do not apply.
  • Integration tests have been added/modified and passed for this PR.
• Documentation
  • This PR introduces no user visible changes.
  • This PR introduces user visible changes and the corresponding documentation change has been made.
• Minor version bump
  • This PR introduces no new features.
  • This PR introduces new features, and there is a separate PR to bump the minor version since the last release already.
  • This PR bumps the version.

[XuechunHou]

Neat! Thanks for working on this Rafael.