Support sending Lobby Invites

[CoreParadox]

Is your feature request related to a problem? Please describe.

Looks like sending lobby invites to a game isn't supported with any of the chat message functions, additionally invites to the client are received as chat_entry_type 1 (ChatMsg).

Describe the solution you'd like

Providing either an overload for sendFriendMessage or a different lobby invite method for sending lobby info: gameId, lobbyId, steamId (where steamId is the lobby host).

Describe alternatives you've considered

Unfortunately any workarounds with sending steam app protocol urls doesn't work as Steam fails to embed links for it's own protocol.