Group PRs in release notes based on labels

[msschwartz21]

Prettier release notes :) Not sure how to test it until we run a release

[DragaDoncila]

@msschwartz21 I think we could test by tagging a release candidate, so you could tag v0.1.2rc0 instead of just v0.1.2. This will go through the full release workflow (including generating release notes), but users installing traccuracy would still get v0.1.1 unless they run pip install --pre traccuracy. If we're not happy with the format we can keep bumping the rc, and then when we are happy, we just tag v0.1.2 and run the full release.

[DragaDoncila]

Approving optimistically and we can edit once we release an rc!