Allow lang-advisors to start FCPs

[tmandry]

FWIW I think it should be ~trivial to adjust rust-lang/team to grant lang-advisors rfcbot permissions (probably add something like https://github.com/rust-lang/team/blob/main/teams/lang.toml#L34-L37 to lang-advisors?), if they don't have them already through some team (many will).

Originally posted by @Mark-Simulacrum in #382 (comment)

[Nadrieril]

(you mean FCPs :) )