[PLT-5864] Move teammate name display setting to the System Console (#6681)

* move teammate name display setting to the system console

* update all the likes of TeammateNameDisplay names

* fix gofmt error

* rebase and fix conflict

model/config.go

@@ -39,6 +39,10 @@ const (
 	DIRECT_MESSAGE_ANY  = "any"
 	DIRECT_MESSAGE_TEAM = "team"
 
+	SHOW_USERNAME          = "username"
+	SHOW_NICKNAME_FULLNAME = "nickname_full_name"
+	SHOW_FULLNAME          = "full_name"
+
 	PERMISSIONS_ALL           = "all"
 	PERMISSIONS_CHANNEL_ADMIN = "channel_admin"
 	PERMISSIONS_TEAM_ADMIN    = "team_admin"
@@ -322,6 +326,7 @@ type TeamSettings struct {
 	UserStatusAwayTimeout               *int64
 	MaxChannelsPerTeam                  *int64
 	MaxNotificationsPerChannel          *int64
+	TeammateNameDisplay                 *string
 }
 
 type LdapSettings struct {
@@ -702,6 +707,11 @@ func (o *Config) SetDefaults() {
 		*o.TeamSettings.MaxNotificationsPerChannel = 1000
 	}
 
+	if o.TeamSettings.TeammateNameDisplay == nil {
+		o.TeamSettings.TeammateNameDisplay = new(string)
+		*o.TeamSettings.TeammateNameDisplay = SHOW_FULLNAME
+	}
+
 	if o.EmailSettings.EnableSignInWithEmail == nil {
 		o.EmailSettings.EnableSignInWithEmail = new(bool)
 
@@ -1394,6 +1404,10 @@ func (o *Config) IsValid() *AppError {
 		return NewLocAppError("Config.IsValid", "model.config.is_valid.restrict_direct_message.app_error", nil, "")
 	}
 
+	if !(*o.TeamSettings.TeammateNameDisplay == SHOW_FULLNAME || *o.TeamSettings.TeammateNameDisplay == SHOW_NICKNAME_FULLNAME || *o.TeamSettings.TeammateNameDisplay == SHOW_USERNAME) {
+		return NewLocAppError("Config.IsValid", "model.config.is_valid.teammate_name_display.app_error", nil, "")
+	}
+
 	if len(o.SqlSettings.AtRestEncryptKey) < 32 {
 		return NewLocAppError("Config.IsValid", "model.config.is_valid.encrypt_sql.app_error", nil, "")
 	}