Switch to git-cliff for changelog generation

[link2xt]

Chatmail core already uses it.

Delta Chat Desktop adopted git-cliff config: deltachat/deltachat-desktop#5639

Once we mark a release, we can switch to using it instead of manually modifying changelog, resolving merge conflicts, adding PR numbers etc.

[link2xt]

1.8.0 is just tagged, main branch is two commits ahead at 1188aed
Changelog still has "untagged" section which apparently corresponds to 1.8.0. (EDIT: fixed in 8715366)
We should at least not merge commits that just say "update ..." (EDIT: abe0cb5 was pushed since I wrote this)

[link2xt]

1.8.0 is tagged with unannotated tag by the way, so git describe still reports 1.1.0-591-gabe0cb5