[NEW] Changes all 'mergeChannels' to 'groupByType'.

[mikaelmello]

Modifies boolean logic as necessary.

It keeps logic reported on #10042 even though I still don't understand it yet.

This PR was made because there were comments with a TODO to do this exact change.

@RocketChat/core

https://github.com/RocketChat/docs/pull/621

[CLAassistant]

All committers have signed the CLA.

[ggazzo]

@mikaelmello shoud we create a migration? what do you think?

[mikaelmello]

@ggazzo Yeah probably. If we don't though, the only impact was that this setting is specific would be kind of "reset", is that correct?

[ggazzo]

something like that, but old servers will keep this useless data forever, and probably some users will complain about loose configs... if you need some help to create a migration I can help :)

[ggazzo]

@mikaelmello I cant checkout your branch could you add this migration?

RocketChat.Migrations.add({
	version: 122,
	up() {
		return RocketChat.models.Users.update({
			'settings.preferences.mergeChannels': {
				$exists: true
			}
		}, {
			$rename: {
				'settings.preferences.mergeChannels': 'settings.preferences.groupByType'
			}
		}, {
			multi: true
		});
	}
});