Add plan collaborators from UI

[dandelany]

Implementation ticket for the design described in #965...

Summary

Users should be able to view, add & remove plan collaborators from the Aerie UI. Requiring users to use graphql to add plan collaborators makes this feature unusable for users who are not proficient at the GQL interface.

Details

The UI for editing plan collaborators should be in the Plan Metadata interface, where parameters are listed. Plan users should only able to view the plan collaborators, while plan owners and admins should also be able to add & remove collaborators

The UI design from @lklyne can be found in this Figma document: https://www.figma.com/file/J86rGzrzuFRAvlGO8ZWKXv/AERIE-%23965-%E2%80%94-Add-plan-collaborator?type=design&node-id=16-1455&mode=design&t=kgajYmJNIRJEK34M-4

Additional design notes from @lklyne:

• Refactor tab input to be used as collaborator selection
• User can search plans and usernames.
• Ideally we'll surface all the recent plans the user accessed as top suggestions. If we don't have access to recents, could consider suggesting based on last modified plans the user has access to?
• List shows plan name on the left, and usernames on the right. The first username should be the plan owner.
• Searching filters plans and usernames. After a search is entered, show username matches on top. (Might need to re-evaluate this one based on some testing. If people do share based on a plan most, this could get in the way.
• Adding a list of usernames from a plan adds that list, but there's no link back to the plan.