[keyserver] Separate webapp and keyserver endpoints

Summary:
Part of ENG-5153
Depends on D9451

Finally we can split the endpoints:

• webapp only hosts html, css, js and other related files
• keyserver contains keyserver logic, websocket etc.

We need to add a redirect for uploads from the webapp to the keyserver because previously the urls had the origin of web.comm.app instead of squadcal.com. As mentioned in the previous diff I don't think it's worth migrating them because:

• we still need to support older clients with old urls
• we will be migrating to blob in the future anyway

Note: landing this diff needs to be delayed like D9291, because web clients need to be reloaded to connect to squadcal

Test Plan:

• check that the web and native apps still work
• check that media with /webapp/ and /comm/ urls still work

Reviewers: inka, kamil, atul

Reviewed By: kamil

Subscribers: ashoat, tomek, wyilio

Differential Revision: https://phab.comm.dev/D9452