docs: Add v0.7.2 release notes

[matthewfeickert]

Description

• Forward port PR docs: Add v0.7.2 release notes #2214 from release/v0.7.x to main.
• Add release notes for pyhf v0.7.2.

Checklist Before Requesting Reviewer

• Tests are passing
• "WIP" removed from the title of the pull request
• Selected an Assignee for the PR to be responsible for the log summary

Before Merging

For the PR Assignees:

• Summarize commit messages into a comprehensive review of the PR

* Forward port PR #2214 from release/v0.7.x to main.
* Add release notes for pyhf v0.7.2.

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (e99733f) 98.30% compared to head (371f542) 98.30%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2218   +/-   ##
=======================================
  Coverage   98.30%   98.30%           
=======================================
  Files          69       69           
  Lines        4533     4533           
  Branches      802      802           
=======================================
  Hits         4456     4456           
  Misses         45       45           
  Partials       32       32           

Flag	Coverage Δ
contrib	97.88% <ø> (ø)
doctest	61.08% <ø> (ø)
unittests-3.10	96.31% <ø> (ø)
unittests-3.11	96.31% <ø> (ø)
unittests-3.8	96.33% <ø> (ø)
unittests-3.9	96.36% <ø> (ø)

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