Replace the 'Coding style proposal' issue template with a MR template

What does this MR do?

This replaces the 'Coding style proposal' issue template with a new 'New static analysis check' MR template instead.

For two reasons:

1. Everything starts with a Merge Request so there's no need to create an issue first.
2. We are not a democratic or consensus driven company

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
• Merge request performance guidelines
• Style guides