Release Automation

Things we could automate with CI or [Github Actions](https://github.com/features/actions):

- create `beta` and `release` branches
- merge from `master` to the branch should trigger the build, sign & publish beta release to AMO and Chrome Web Store
- caveat: firefox Beta is self-hosted and requires publishing `.xpi` + updating [this manifest](https://github.com/ipfs-shipyard/ipfs-companion/blob/master/ci/firefox/update.json)

Ref.
- Firefox signing
- https://github.com/kewisch/action-web-ext/
– upload and publish browser extensions to the Chrome web store
- https://github.com/marketplace/actions/chrome-extension-upload-action
- https://github.com/marketplace/actions/chrome-extension-upload-publish