Restructure Bot repos under a new gerrit namespace

It's often difficult to figure out where to put a new bot within the existing repos. While they often end up in qt/qtqa, I'm not sure that's really the right place, and these internal (but public code) bots don't need to be distributed with Qt. Including them in nested directories of qtqa also complicates the deployment and execution of the bots, as some cloud-hosted services like Heroku are unable to execute anything other than a top-level target.

Proposed namespace "qtbots/"
This structure would enable creation of repos like:
qtbots/qtcherrypickbot
qtbots/submoduleupdatebot
qtbots/insignificantwatcherbot (Will not move as of now. Is not a bot, and has hard-coded values. needs cleanup and unification.)
qtbots/corebenchmarksbot
qtbots/flake8bot

and so on...