Docs: Add information to create a merge request page

Suggestion to add content to the creating_merge_requests.md page:

• In Add create MR to work item branch (!181479 - merged), the new functionality is building on top of the existing linked branch capabilities. I think this would make the most sense with this reorganization to add in creating_merge_requests.md under "From an issue" and "From a task", below the existing guidance, I added an idea for this below. If you merge this to master, I can add this as a follow-up.

  To create a merge request when the branch is already linked in Development:

  1. On the left sidebar, select Search or go to and find your project.
  2. Select Plan > Issues.
  3. In the issue list, find your task.
  4. Find the branch within the Development list
  5. Open the branch actions menu
  6. Select Create merge request

• For issues, this new feature (just this one button to create an MR from an already linked branch) is dependent on the "New look: On" beta toggle, which is controlled by a feature flag. Tasks will be available immediately.

Related issues

• Add create MR to work item branch (!181479 - merged)
• Shift branch-only instructions to branches page (!184852 - merged)
• Development Widget: Create MR from linked Branch (#519655 - closed)