docs: Add v0.7.4 release notes

[matthewfeickert]

Description

• Forward port PR docs: Add v0.7.4 release notes #2322 from release/v0.7.x to main.
• Add release notes for pyhf v0.7.4.

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 #2322 from release/v0.7.x to main.
* Add release notes for pyhf v0.7.4.

[matthewfeickert]

Relvant RTD docs: https://pyhf--2330.org.readthedocs.build/en/2330/release-notes.html#release-v0-7-4

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (f771581) 98.28% compared to head (b4c3a0b) 98.28%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2330   +/-   ##
=======================================
  Coverage   98.28%   98.28%           
=======================================
  Files          69       69           
  Lines        4538     4538           
  Branches      803      803           
=======================================
  Hits         4460     4460           
  Misses         45       45           
  Partials       33       33           

Flag	Coverage Δ
contrib	97.86% <ø> (ø)
doctest	60.99% <ø> (ø)
unittests-3.10	96.29% <ø> (ø)
unittests-3.11	96.29% <ø> (ø)
unittests-3.8	96.31% <ø> (ø)
unittests-3.9	?

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