dev: workaround docker hub rate limiting

Created by: michaellzc

Part of https://github.com/sourcegraph/sourcegraph/issues/30758

Port https://github.com/sourcegraph/update-docker-tags/pull/3 in sg-cli

pardon my horrible go knowledge, feel free to let me know if there is a better way to implement this.

How to test

cd dev/sg
go build .

Go to deploy-sourcegraph, and run (you can run 10 times in a row without getting rate limited)

/path/to/sg ops update-images base/.

The command will try to reuse your docker credentials store. You can verify it by inspecting the logs before and after docker logout

You should see files in base/ are getting updated as expected