Open source checklist

- [x] Rename project (#186)
- [x] Update all repos to use `.mergit.yaml`
- [x] Remove logic in `extractConfig`
- [x] Break out developer-specific README from user-focused README (copy things over from Notion runbook)
- [x] Move issues from JIRA into Github issues (reopen issues if relevant)
- [x] Remove references to internal URLs + channels (JIRA, Notion, Slack)
- [x] Remove LeapYear-specific references/docs/code
- [ ] Break out public repo
- Rename this repo to `mergit-deploy`
- Create public repo named `mergit`
- Copy issues over manually (don't transfer, to avoid including the comments mentioning JIRA. it's not that big of a deal, but it'd be cleaner to not show all of that churn)
- Don't copy over issues related to _our_ hosted mergit instance (e.g. the issues tagged "infrastructure")
- Copy code over
- Delete `deploy/` directory
- Squash git history
- Add tickets to `mergit-deploy`:
- Replace terraform scripts with scripts that deploy docker (blocked on #205)
- Move into `infrastructure` repo?
- Move tickets into JIRA?
- Make dockerhub repo public: https://hub.docker.com/repository/docker/leapyear1/mergit/general