Add GitHub Actions for releasing fleetd-chrome beta and production. See
the included README updates for details.
This was tested with an `on: pull-request` trigger for the beta workflow
which is now removed for merging into the repo.
# Checklist for submitter
If some of the following don't apply, delete the relevant line.
- [x] Changes file added for user-visible changes in `changes/` or
`orbit/changes/`.
See [Changes
files](https://fleetdm.com/docs/contributing/committing-changes#changes-files)
for more information.
- [x] Added/updated tests
- [x] Manual QA for all new/changed functionality