Rollup merge of #134669 - clubby789:dev-ci-mode, r=jieyouxu

Document the `--dev` flag for `src/ci/docker/run.sh`

This flag is very helpful for debugging CI issues locally, but it's not documented anywhere and I wasn't aware of it until `@jieyouxu` pointed it out. Add a note to the CI Docker readme to make this more discoverable

Author: matthiaskrgr