docs: Add developer release checklist Issue template

[matthewfeickert]

Description

Resolves #1319

Add a developer release checklist Issue Template to make sure that steps don't get missed during the release and to formalize the release so that any member of the developer team can do it.

Restrict the issue template to project maintainers only. c.f. https://github.com/pypa/pip/blob/e6414d6db6db37951988f6f2b11ec530ed0b191d/.github/ISSUE_TEMPLATE/~good-first-issue.md for an example.

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

* Add a developer release checklist GitHub Issue template
   - Restrict the Issue template to be usable by project maintainers only
* Add a section to the development docs mentioning the Issue template

[codecov]

Codecov Report

Merging #1493 (018666e) into master (302af0b) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1493   +/-   ##
=======================================
  Coverage   97.65%   97.65%           
=======================================
  Files          63       63           
  Lines        4006     4006           
  Branches      565      565           
=======================================
  Hits         3912     3912           
  Misses         55       55           
  Partials       39       39           

Flag	Coverage Δ
contrib	25.51% <ø> (ø)
unittests	97.42% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 302af0b...018666e. Read the comment docs.

[matthewfeickert]

Relevant page for review: https://pyhf--1493.org.readthedocs.build/en/1493/development.html

[kratsg]

Shouldn't we add an ISSUE_TEMPLATE for release checklist instead? I'm not sure it needs to be added to the docs explicitly but...

[matthewfeickert]

Shouldn't we add an ISSUE_TEMPLATE for release checklist instead? I'm not sure it needs to be added to the docs explicitly but...

Yeah, that's a much better idea. I originally had this as part of a PR comment, but then changed to an Issue. I'll fix this up. 👍

[matthewfeickert]

Probably easiest way to review online is to read here: https://github.com/scikit-hep/pyhf/blob/docs/add-developer-release-checklist/.github/ISSUE_TEMPLATE/~release-checklist.md