[CLAN APP] Be able to add Managers to a clan to be able to create Invite links / Approve join requests

[Rackover]

Reported by @MrRowey here https://github.com/FAForever/website/issues/322 Please fill in with more details / examples / repro steps if any 🙂

[fcaps]

this also needs changes in the java api, you need to change it there first