[Quest API] Add IsInAGuild() to Perl/Lua (#4066)

# Perl
- Add `$client->IsInAGuild()`.

# Lua
- Add `client:IsInAGuild()`.

# Notes
- Allows operators to more accurately tell if a player is in a group.
- `GuildID()` returns `uint32` max value if the player isn't in a guild so conditions using it must check for a value over a certain point, this is just a bool that simplifies that logic.

zone/lua_client.h

@@ -495,6 +495,7 @@ public:
 	void ClearXTargets();
 	int GetAAEXPPercentage();
 	int GetEXPPercentage();
+	bool IsInAGuild();
 
 	void ApplySpell(int spell_id);
 	void ApplySpell(int spell_id, int duration);