Add a script to run gerrit commands on the depot host, which reads the
gerrit username from the TVL_USERNAME env var or $(whoami) by default.
At some point this may want to solve the configuration problem in a more
general fashion, but for now this seems relatively obvious.
Change-Id: Ied91c1d26daf4770aef74b2e755d1760c486bb7b
Reviewed-on: https://cl.tvl.fyi/c/depot/+/396
Reviewed-by: tazjin <mail@tazj.in>
Reviewed-by: glittershark <grfn@gws.fyi>