Get Teammangers by Clan

[hoersamu]

• rename DISCORD_CLIENT_ID and DISCORD_CLIENT_SECRET to DISCORD_OAUTH_CLIENT_ID and DISCORD_OAUTH_CLIENT_SECRET
• add new env variables DISCORD_BOT_CLIENT_ID and DISCORD_BOT_CLIENT_SECRET
• add new endpoint /clans/[oid]/managers that returns the following schema:
  [{id:string, username: string, avatar: string}]

There is no API endpoint for automatically filtering by role so we'll need to fetch all members and manually filter by role. This endpoint should be implemented in the "combined" mode (e.g. only on class for PC and Console (see search)).