We need to use bazelisk to build gerrit so that we can properly
track bazel versions in the job. Use the roles developed for
gerrit-review to do that, then simplify the dockerfile to have
it simply copy the war into the target image.
Also add polymer-bridges.
Depends-On: https://review.opendev.org/709256
Change-Id: I7c13df51d3b8c117bcc9aab9caad59687471d622