Stop using CHANGELOG and move to GitHub release notes

[yanokwa]

Following up on the conversation at https://github.com/enketo/enketo-express/pull/338#issuecomment-948768093 with @lognaturel and @jnm.

I'd like to have a more consistent process across all the tools we are maintaining and so I'd prefer to stop use of the CHANGELOG and lean more heavily on automated GitHub release notes going forward.

I think between the commits, the new PR template, and PR title, there's enough there for the maintainer (typically the person doing the release) to adjust the release notes if necessary. I think those adjustments are necessary because the maintainer as a lot more context about the impact of the changes.

@eyelidlessness @seadowg Any thoughts on this?

[eyelidlessness]

I think I'm good with this, but I think we should still have a review process. Which in this case would probably look like saving a draft for "review". Mainly because another set of eyes has already caught cases where there was more context in another issue or similar.

[seadowg]

👍. Like this.

As a side note the automated release notes didn't quite work for me last time as they seem to include everything from the last full release (not the last pre release) so if you're doing betas they're a little clunky currently. I've just been using git log --first-parent and then moving up from the last release tag to build notes.