Cleanup issue and PR templates for easier use

[jadchaar]

Pull Request Checklist

Thank you for taking the time to improve Arrow! Before submitting your pull request, please check all appropriate boxes:

• [ ] 🧪 Added tests for changed code.
• [ ] 🛠️ All tests pass when run locally (run tox or make test to find out!).
• [ ] 🧹 All linting checks pass when run locally (run tox -e lint or make lint to find out!).
• [ ] 📚 Updated documentation for changed code.
• [x] ⏩ Code is up-to-date with the master branch.

If you have any questions about your code changes or any of the points above, please submit your questions along with the pull request and we will try our best to help!

Description of Changes

In the past, we have seen people struggle to follow the PR and issue templates (e.g. place things inside of the HTML comments), so I have cleaned them up to make them a bit easier to navigate and use.

[codecov[bot]]

Codecov Report

Merging #859 into master will not change coverage. The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #859   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            9         9           
  Lines         1808      1808           
  Branches       312       312           
=========================================
  Hits          1808      1808           

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