Enhancement issue template

[charlestian23]

Description

This pull requests adds another issue template for enhancements. This separates the templates for new features and enhancements and allows us to ask questions specific to new features or enhancements.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Enhancement (improvement to an already existing feature)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

How Has This Been Tested?

GitHub allows you to preview the template here: https://github.com/Bram-Hub/Legup/blob/enhancement-issue-template/.github/ISSUE_TEMPLATE/enhancement_request.yml

You can visit the page to "test" the template if you make any changes to it.

Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (if applicable)
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes