Updates PR Template to include Version label

[supernova-at]

Description

This PR updates our pull request template to add a checklist step for PR authors to propose a SemVer change level of their changes (patch, minor, major).

Related Issue

Closes #1047 .

Motivation and Context

We'd like to determine MAJOR, MINOR, or PATCH changes at the PR level while we have context into the change instead of at release time when it will be easier to forget or miss the impact of a change.

Three new labels exist for this purpose:

1. version: Major
2. version: Minor
3. version: Patch

To get PR authors to add these labels, this PR adds a step to the PR checklist.

Verification

Reading the new PR Template for accuracy.

How Has This Been Tested?

n/a

Screenshots (if appropriate):

Proposed Labels for Change Type/Package

DOCUMENTATION

n/a

Checklist:

• I have read the CONTRIBUTING document.
• I have linked an issue to this PR.
• I have indicated the change type and relevant package(s).
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.
• All CI checks are green (linting, build/deploy, etc).
• At least one core contributor has approved this PR.

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[coveralls]

Coverage remained the same at 76.672% when pulling 9596775 on supernova/1047-add_version_label_to_pr_template into 822591e on develop.

[supernova-at]

I added / fixed up a couple other minor things in the PR Template while I was in there.

I don't know how / that we're using the answers to the "Proposed Labels for Change Type/Package" question, so that could be a good one to drop. That change seemed out of scope for this ticket though.

[jcalcaben]

I agree with dropping the labels/package question. I also propose dropping the last two checkbox items as they will never be checked on initial create.

[tjwiebell]

LGTM, but wanted to check if we want to sneak the removal of those two loosely used checkboxes in the scope of this PR. I'm leaning towards no, and we just merge. @supernova-at, agree?