Consider adding GH templates for issues and PRs

[tomvothecoder]

I found that using templates for issues and PRs makes it easier to scope requirements and track progress in a consistent manner.

I've added templates for xCDAT here that we can port over:

• Issues: https://github.com/xCDAT/xcdat/tree/main/.github/ISSUE_TEMPLATE
  • Example: https://github.com/xCDAT/xcdat/issues/435
• PRs: https://github.com/xCDAT/xcdat/blob/main/.github/pull_request_template.md
  • Example: https://github.com/xCDAT/xcdat/pull/418

[tomvothecoder]

Duplicate of #702