Automated changelog generation

[dhess]

Ref:

• https://github.com/semantic-release/semantic-release
• https://github.com/semantic-release/release-notes-generator
• https://github.com/amannn/action-semantic-pull-request
• https://github.com/conventional-changelog/commitlint

[dhess]

Some of these tools rely on a particular commit message format, and this might be problematic when used together with GitHub merge queues; see, e.g., https://github.com/orgs/community/discussions/46757#discussioncomment-4919578

I think we'll be OK so long as we enable the "use PR title and OP comment" commit message feature of merge queues, assuming we can ensure those are formatted correctly. (Having said that, I don't see an option for the commit message format in our project settings, though I'm sure it was previously available. I'll investigate. Edit: found it, it's here under Pull Requests, and is a setting independent of merge queues. edit 2: this merge message format is now enforced on this repo (and all of our others, as well).)