Update versions and CHANGELOG for 5.1.0 release

[alamb]

Note this targets the active_release branch

I want to see if I can get a clean CI run before creating a release candidate for 5.1.0 -- active release is still failing due to #631 (I just need to back port it)

[codecov-commenter]

Codecov Report

Merging #632 (17d1b03) into active_release (6d222fa) will not change coverage.
The diff coverage is n/a.

❗ Current head 17d1b03 differs from pull request most recent head 4e57b5d. Consider uploading reports for the commit 4e57b5d to get more accurate results

@@               Coverage Diff               @@
##           active_release     #632   +/-   ##
===============================================
  Coverage           82.48%   82.48%           
===============================================
  Files                 167      167           
  Lines               46450    46450           
===============================================
  Hits                38312    38312           
  Misses               8138     8138           

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