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.

model/config.go

@@ -354,6 +354,7 @@ type TeamSettings struct {
 	MaxChannelsPerTeam                  *int64
 	MaxNotificationsPerChannel          *int64
 	TeammateNameDisplay                 *string
+	ExperimentalTownSquareIsReadOnly    *bool
 }
 
 type ClientRequirements struct {
@@ -824,6 +825,11 @@ func (o *Config) SetDefaults() {
 		*o.TeamSettings.MaxNotificationsPerChannel = 1000
 	}
 
+	if o.TeamSettings.ExperimentalTownSquareIsReadOnly == nil {
+		o.TeamSettings.ExperimentalTownSquareIsReadOnly = new(bool)
+		*o.TeamSettings.ExperimentalTownSquareIsReadOnly = false
+	}
+
 	if o.EmailSettings.EnableSignInWithEmail == nil {
 		o.EmailSettings.EnableSignInWithEmail = new(bool)