[web] Create manage links modal

Summary:
A modal where links can be managed
https://www.figma.com/file/a1nkbWgbgjRlrOY9LVurTz/Comm-%2F-Desktop-app?node-id=11400%3A288445&mode=dev
https://www.figma.com/file/a1nkbWgbgjRlrOY9LVurTz/Comm-%2F-Desktop-app?node-id=11341%3A282899&mode=dev

Depends on D8412

Test Plan: Click manage links button and check if the modal is correct, both when a public link is present and when a community doesn't have a link.

Reviewers: bartek, kamil, inka, ashoat

Reviewed By: ashoat

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D8413