Add x to be able to leave public and private channels (#7145)

* Add config value EnableXToLeaveChannelsFromLHS that if true displays x to the right of private and public channels on the LHS.

* Displays x to the right of private and public channels on the LHS based on if EnableXToLeaveChannelsFromLHS=true.

* change the tooltip for private and public channels to `Leave channel`

* Add client-side event for when user clicks the "x" button. Different for public, private, DM.

utils/config.go

@@ -438,6 +438,7 @@ func getClientConfig(c *model.Config) map[string]string {
 	props["RestrictPublicChannelDeletion"] = *c.TeamSettings.RestrictPublicChannelDeletion
 	props["RestrictPrivateChannelDeletion"] = *c.TeamSettings.RestrictPrivateChannelDeletion
 	props["RestrictPrivateChannelManageMembers"] = *c.TeamSettings.RestrictPrivateChannelManageMembers
+	props["EnableXToLeaveChannelsFromLHS"] = strconv.FormatBool(*c.TeamSettings.EnableXToLeaveChannelsFromLHS)
 	props["TeammateNameDisplay"] = *c.TeamSettings.TeammateNameDisplay
 
 	props["AndroidLatestVersion"] = c.ClientRequirements.AndroidLatestVersion