Resolve "Default Web IDE's merge request checkbox to true"

What does this MR do?

• Pull the new MR option out into it's own component
• Default MR checkbox to true when creating a new MR and committing to a branch that does not have an MR
• Still change the MR checkbox to false when a user is on a branch that already has an MR
• Hide MR option when on a branch that already has an MR and committing to current branch
• Don't default to true when committing directly to master

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry \
• Code review guidelines
• Style guides

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Closes #60034 (closed)