Move preference button to left of the create merge request button

Proposal

Move the preference icon button to the left of the create merge request page on the merge request homepage.

• Making this change adheres to Pajamas guidance on button order.
• We would be interested to see if there is an increase in preferences interaction post change.

More context on this change https://gitlab.com/gitlab-org/gitlab/-/issues/519717/designs/Labels_and_groups.png#note_2397904725