MM-35332 honour config setting when extending session expiry (#17581)

Honour `ServiceSettings.ExtendSessionLengthWithActivity` config setting when extending session expiry on activity.

app/session.go

@@ -351,6 +351,10 @@ func (a *App) UpdateLastActivityAtIfNeeded(session model.Session) {
 // A new ExpiresAt is only written if enough time has elapsed since last update.
 // Returns true only if the session was extended.
 func (a *App) ExtendSessionExpiryIfNeeded(session *model.Session) bool {
+	if !*a.Srv().Config().ServiceSettings.ExtendSessionLengthWithActivity {
+		return false
+	}
+
 	if session == nil || session.IsExpired() {
 		return false
 	}