Move "Promote" to actions menu for milestone list pages

What does this MR do and why?

Removes the Promote button shown on milestone list pages and adds an action menu that includes edit, promote and delete actions depending on context.

MR acceptance checklist

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Screenshots or screen recordings

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Page	Before	After
Individual Milestone page in a project (no change)
Individual Milestone page in a group (no change)
Project milestone list page
Group milestone list page
Your work Milestone Dashboard list page

How to set up and validate locally

1. Check out this branch locally
2. Restart your GDK. This is necessary in order to get the newly added index.js page added to the bundle.
3. Visit a project milestones page
   1. You will see that there is a "Milestone actions" vertical-ellipse dropdown button on all the milestones. The "Promote to group milestone" icon button is no longer present.
   2. Open the milestone actions menu and you will see options to Close, Edit, Promote and Delete the milestone
   3. If you click edit, you will navigate to the edit page for the milestone
   4. If you click Promote, you will get a modal that checks if you are sure
      1. If you click "Promote milestone" in the modal, the milestone will be successfully promoted to a group milestone.
   5. If you click Delete, you will get a modal that checks if you are sure
      1. If you click "Delete milestone" in the modal, the milestone will be successfully deleted.
4. Visit a group milestones page
   1. You will see that there is a "Milestone actions" vertical-ellipse dropdown button on all the milestones.
   2. Open the milestone actions menu and you will see options to Close, Edit and Delete the milestone
      1. The Milestone cannot be promoted from this page. There is no Promote option in the menu.
      2. If you click edit, you will navigate to the edit page for the milestone
      3. If you click Delete, you will get a modal that checks if you are sure
         1. If you click "Delete milestone" in the modal, the milestone will be successfully deleted.
5. Visit the your work/milestones page
   1. You will see that there is a "Milestone actions" vertical-ellipse dropdown button on all the milestones.
      1. The menu has options to Close and Edit the milestone.
      2. The milestone cannot be promoted (if a project milestone) or deleted from here.
   2. If you click on one of the milestone action dropdown buttons, it will open a dropdown that only contains an Edit option
   3. If you click edit, you will navigate to the edit page for the milestone

Related to #396753 (closed), #425467 (closed)