Merge request drop down in the top bar and MR section of `Your Work` should also have an `Authored` option

Proposal

Currently, the MR drop down in the top bar and section in Your Work has an Assigned and Review requests option. Given MRs don't auto-assign to the author (see #355753 (closed) and #355753 (comment 924886933) for context), it is easy to "lose" an MR you're working on if you forget to assign it to yourself.

It'd be nice to have a top-level Authored item to have all MRs you've authored but may not be the assignee of.