feat: Enable updating of MR notes

Description

This MR extends the existing mr command to allow updating existing comments. The functionality already exists in the go-gitlab package, this MR just wires it in.

It is added as a flag to the existing command rather than a new sub command - feedback requested on this design choice!

Related Issues

Resolves #1198

How has this been tested?

• This has been unit tested.
• This has been tested with a local GDK install, using the CLI to create a note on an MR and then update it.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation
• Chore (Related to CI or Packaging to platforms)
• Test gap