Update merge request templates for front / engine

Wanting to collect ideas of how we could utilize merge request templates to improve communication and aide in planning against regressions. Totally open to suggestions on what additional fields we could have in there - current template has [paraphrased]:

• Summary
• Steps for testing
• Regression Scope

Suggested additions to consider:

• Impact on mobile app - more applicable to the engine, though front-end could still be relevant to discuss whether parity is necessary.
• Deployment strategy - Some changes should be rolled out to Canary, some changes need to be rolled out all at once to production etc.
• Test Coverage - Covered in the actual code, but possibly worth considering to act as a reminder.