Adds support for GMs in shared channels (#31403)

* Adds support for GMs in shared channels

* Fix linter

* Remove creatorID from slack call

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Co-authored-by: Miguel de la Cruz <miguel@ctrlz.es>

server/channels/store/store.go

@@ -188,7 +188,7 @@ type TeamStore interface {
 }
 
 type ChannelStore interface {
-	Save(rctx request.CTX, channel *model.Channel, maxChannelsPerTeam int64) (*model.Channel, error)
+	Save(rctx request.CTX, channel *model.Channel, maxChannelsPerTeam int64, channelOptions ...model.ChannelOption) (*model.Channel, error)
 	CreateDirectChannel(ctx request.CTX, userID *model.User, otherUserID *model.User, channelOptions ...model.ChannelOption) (*model.Channel, error)
 	SaveDirectChannel(ctx request.CTX, channel *model.Channel, member1 *model.ChannelMember, member2 *model.ChannelMember) (*model.Channel, error)
 	Update(ctx request.CTX, channel *model.Channel) (*model.Channel, error)