ci: automatic release management

[mrcjkb]

Closes #30

Will create release PRs, bumping the version and adding changelog entries, based on conventional commits.

Currently, conventional commits are not enforced. I haven't yet found a way to do so in a way that works nicely with the release-please workflow.
If people contribute with non-conventional commits, you can make the PR title CC compliant, and squash merge.

• You may also need to set "Allow GitHub Actions to create and approve pull requests" under repository Settings > Actions > General.

[mrcjkb]

Marking as draft again. There is still an issue with the workflow failing because it expects tags and then not creating a release PR.

[mrcjkb]

I had to revert back to giving each crate its own version, because release-please doesn't seem to support workspace.version.

See also: googleapis/release-please#2111

Here's an example of what a release PR looks like: mrcjkb#3

It currently updates the changelog in each crate, but I think we can live with that until release-please supports workspace.version.

[AaronErhardt]

Looks good. Anything left to do before merging?

Btw. for the future, we could consider adding automatic crates.io releases.

[mrcjkb]

Looks good. Anything left to do before merging?

Btw. for the future, we could consider adding automatic crates.io releases.

I think it's good to merge now.
Might need some refinement, but I can do that in a follow-up.

crates.io releases sounds like a good idea too 😃

[AaronErhardt]

Thanks!