Summary:
Currently tags are copied after a copybara trigger, which only happens
on pushes. Instead add a multibranch pipeline to Jenkins that also triggers
copybara. This will ensure that tags get copied over even without a commit
being pushed to the repo.

Test Plan: Run it in Jenkins

Reviewers: zasgar, michelle

Reviewed By: michelle
Signed-off-by: Copybara <copybara@pixielabs.ai>

Differential Revision: https://phab.corp.pixielabs.ai/D11649

GitOrigin-RevId: 15ba5c7abe473c64356451f47d16320c2a8c61fd