Config to make town square read only (#7140)

* Be able to make Town Square read-only (Disable typing messages for non admins).

* Do not emit UserTypingEvent when TownSquareIsReadOnly and is Town Square.

* Add unit tests for TownSquareIsReadOnly config value and logic.

* Add TownSquareIsReadOnly to System console>Policy. Added Telemetry.

* Add control for TownSquareIsReadOnly=true only for License Enterprise Edition E10 & E20.

* Update en.json

* Update en.json

* Update policy_settings.jsx

* Change config value from TownSquareIsReadOnly to ExperimentalTownSquareIsReadOnly.

* Refactored to simplify. Avoid code repeat and multiple db calls.

app/diagnostics.go

@@ -243,6 +243,7 @@ func trackConfig() {
 		"isdefault_custom_description_text":       isDefault(*utils.Cfg.TeamSettings.CustomDescriptionText, model.TEAM_SETTINGS_DEFAULT_CUSTOM_DESCRIPTION_TEXT),
 		"isdefault_user_status_away_timeout":      isDefault(*utils.Cfg.TeamSettings.UserStatusAwayTimeout, model.TEAM_SETTINGS_DEFAULT_USER_STATUS_AWAY_TIMEOUT),
 		"restrict_private_channel_manage_members": *utils.Cfg.TeamSettings.RestrictPrivateChannelManageMembers,
+		"experimental_town_square_is_read_only":   *utils.Cfg.TeamSettings.ExperimentalTownSquareIsReadOnly,
 	})
 
 	SendDiagnostic(TRACK_CONFIG_CLIENT_REQ, map[string]interface{}{