Simplify the PR template, add checkboxes, remove redundant info

[nkolev92]

Bug

Fixes: https://github.com/NuGet/Client.Engineering/issues/432
Regression: No

• Last working version:
• How are we preventing it in future:

Fix

Details:
@zivkan suggested using https://github.com/PowerShell/PowerShell/blob/master/.github/PULL_REQUEST_TEMPLATE.md as inspiration.
Simplifying the PR template.

• Retain only relevant information and make it easy for the contributor to honor the template (ex. using checkboxes instead of having to replace text.)

• Keep it relatively simple (not super thrilled about the length), as large templates are .

• Any feedback welcome 👍 I created this PR to start a conversation.

Testing/Validation

Tests Added: No
Reason for not adding tests:
Validation:

[zivkan]

I like it 👍

Only comment is that the checklists will cause the PR view to claim the PRs have completed "5/8 tasks", or something like that. Not a big deal, we'll just need to learn to live with it, and I don't really have any better suggestion.

<-- Delete all but one -->
Tests: Automated tests added
Tests: Test exception
Tests: N/A

Tests: [Automated tests added|Test exception|N/A]

Tests: Automated tests added **OR** Test exception **OR** N/A

I think your template is most likely to have contributors do what we want.

[nkolev92]

Only comment is that the checklists will cause the PR view to claim the PRs have completed "5/8 tasks", or something like that. Not a big deal, we'll just need to learn to live with it, and I don't really have any better suggestion.

Yeah, I had the same thought.
There's just no way to create a radio box in markdown right now.