Added join_team schema for join requests.
Added join_team schema for join requests.

cganas/picoCTF-web,picoCTF/picoCTF-web,alpire/picoCTF-web,alpire/picoCTF-web,picoCTF/picoCTF-web,cganas/picoCTF-web,alpire/picoCTF-web,picoCTF/picoCTF-web,picoCTF/picoCTF-web,alpire/picoCTF-web,cganas/picoCTF-web,cganas/picoCTF-web