Refactor rest-client-module

2020-03-13 16:27:56,865 TRACE class org.ehcache.core.Ehcache-REST_CLIENT_CACHE : Initializing
2020-03-13 16:27:56,866 DEBUG class org.ehcache.core.Ehcache-REST_CLIENT_CACHE : Initialize successful.
2020-03-13 16:29:20,378 WARN org.jboss.resteasy.resteasy_jaxrs.i18n : RESTEASY002160: Provider instance info.magnolia.rest.client.app.ui.debug.DebugFilter is already registered. 2nd registration is being ignored.
2020-03-13 16:37:48,575 WARN org.jboss.resteasy.client.jaxrs.i18n : RESTEASY004687: Closing a class org.jboss.resteasy.client.jaxrs.engines.ApacheHttpClient43Engine instance for you. Please close clients yourself.
2020-03-13 16:37:48,576 WARN org.jboss.resteasy.client.jaxrs.i18n : RESTEASY004687: Closing a class org.jboss.resteasy.client.jaxrs.engines.ApacheHttpClient43Engine instance for you. Please close clients yourself.

info.magnolia.rest.client.app.ui.debug.DebugFilter is already registered. 2nd registration is being ignored.

After discussed with dai.ha, this log entry could be ignored since it causes no harm.

Criteria:

• Refactor RestClient, RestClientFactory:
  • Do not expose Client, WebTarget to user
  • Client should be closed after used via RestClient's api
  • All cached Client should be closed when module is stopped
  • Custom Filter could be register on demand via RestClient's api
• Using RestClient:
  • Share RestClient should be cached and handled by RestClientProvider
  • RestClient which is not cached should be closed right after used
• Register custom filter on demand
  • RestClient allows to register/unregister custom filter without expose jaxrs Client or WebTarget