Add KeepQuotedReply option for matrix to fix regression (#1823)

Matrix quotes replies and as of matterbridge 1.24.0 we strip those as this causes
issues with bridges support threading and have PreserveThreading enabled.

Introduced via https://github.com/42wim/matterbridge/commit/9a8ce9b17e560433731eb5efa3cee7ced0b93605

But if you for example use mattermost or discord with webhooks you'll need to enable
this if you want something that looks like a reply from matrix.
See issues:
- https://github.com/42wim/matterbridge/issues/1819
- https://github.com/42wim/matterbridge/issues/1780

bridge/mattermost/helpers.go

@@ -183,6 +183,7 @@ func (b *Bmattermost) sendWebhook(msg config.Message) (string, error) {
 	if b.GetBool("PrefixMessagesWithNick") {
 		msg.Text = msg.Username + msg.Text
 	}
+
 	if msg.Extra != nil {
 		// this sends a message only if we received a config.EVENT_FILE_FAILURE_SIZE
 		for _, rmsg := range helper.HandleExtra(&msg, b.General) {