[JENKINS:SECURITY-1153] Monitoring Plugin did not apply CSRF protection even if enabled in Jenkins

Monitoring Plugin provides a standalone JavaMelody servlet with an independent CSRF protection configuration.
Even if Jenkins had CSRF protection enabled, Monitoring Plugin may not have it enabled.

Monitoring Plugin now checks on startup whether Jenkins has CSRF protection enabled and enables its own CSRF protection accordingly.

NOTE: Monitoring Plugin does not take into account configuration changes applied after Jenkins startup or after Monitoring Plugin finishes loading.
Administrators need to restart Jenkins when enabling or disabling the CSRF protection configuration to apply the change to Monitoring Plugin.