[Feature Requeat] Make join/leave notifications being relayed optional

[balasankarc]

Consider a Telegram<=>Matrix<=>IRC setup. From the telegram side, it can be irritating to get all the "XYZ (IRC) joined room" messages from IRC.

It may be good to make this notification optional, based on a feature flag or env variable.

[kannanvm]

This is really necessary, I just deleted more than hundred irc notification altogether. Its getting annoying in some groups and it should be made optional.