Add jaxws-endpoint-configuration to AS7 domain

This feature request is about adding support for jaxws endpoint configurations to the AS7 domain model. We used to have them in the standard-jaxws-endpoint.xml file before AS7 and for jbossws-native only. Now, after JBWS-3282 work, we do have a stack agnostic jaxws endpoint configuration concept. jbossws-spi has the xsd and parser for that. Currently @EndpointConfig can be used to reference a descriptor provided with the deployment and containing the endpoint configuration to be used. If the annotation is not specified, jbossws-native defaults to the contents of standard-jaxws-endpoint.xml, while jbossws-cxf defaults to no configuration (see org.jboss.wsf.stack.cxf.metadata.MetadataBuilder::configureEndpoint(..) ).
So we need to:
1) expose a mean of getting the default jaxws endpoint configurations in jbossws-spi
2) use that in jbossws-cxf MetadataBuilder and in jbossws-native org.jboss.ws.metadata.config.JBossWSConfigFactory
3) actually add the jaxws-endpoint-configuration to AS7 detyped model

In terms of AS7 management, it should be possible to add/delete/modify a given default jaxws endpoint configuration. An all-or-nothing update policy might make sense for the contents of the handlers section of each endpoint configuration.