In preparation for the v0.37 release, this PR updates:
1. The [release guidelines](https://github.com/tendermint/tendermint/blob/thane/pre-release-workflows/RELEASES.md#pre-releases) regarding alpha and beta versions, as well as release candidates.
2. The GitHub workflows to build all 3 kinds of pre-releases for:
1. Docker images
2. Binaries (I'm still not 100% sure whether this is necessary, but it does act as a clear signal to users that a pre-release is available, and pre-built binaries could be useful for people running testnets who don't use Docker)
3. The Goreleaser config to auto-detect whether a tag is a pre-release and mark it as such as the release is created on GitHub.
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#### PR checklist
- [x] Tests written/updated, or no tests needed
- [x] `CHANGELOG_PENDING.md` updated, or no changelog entry needed
- [x] Updated relevant documentation (`docs/`) and code comments, or no
documentation updates needed
