Provide explicit contextId for AdminServerApplication

- Add AdminIdInitializer that sets the adminContextId explicitly
Override XD MBean exporters' domain names

- Exclude JmxAutoConfiguration so that Integration MBean exporters defined in configuration classes based on the conditional
expression ${XD_JMX_ENABLED:true} get to set their domain name
  - With this change,
     - the XD container will have MBeans with domain names `xd.parent`, `xd.shared.server` and `xd.container`
     - the XD admin will have MBeans with domain names `xd.parent', `xd.shared.server` and `xd.admin`
     - the XD singlenode will have all the MBeans above