Conflicts:
- `CHANGELOG.md`:
Upstream added newlines.
Conflicts are because the CHANGELOG was independently merged from 3.4.6 on
last security update.
Took upstream's version.
- `app/helpers/context_helper.rb`:
Conflicts because of extra vocabulary in glitch-soc. The conflicts were
actually handled in last security merge.
Kept our version.
* Build container image by GitHub Actions
* Trigger docker build only pushed to main branch
* Tweak tagging imgae
- "edge" is the main branch
- "latest" is the tagged latest release
