chore/3.1.6 release notes (#3790)

* have towncrier use h2 header for each release note

* remove h1 headers

* release notes

* rebuild release notes docs with #3769

* add more release notes

* style

* Update release-notes.md

Co-authored-by: Max Jones <14077947+maxrjones@users.noreply.github.com>

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Co-authored-by: Max Jones <14077947+maxrjones@users.noreply.github.com>

Author: d-v-b