Enhance README of ejb-remote quickstart to be easier to setup the server

The `ejb-remote` quickstart (https://github.com/wildfly/quickstart/tree/19.0.0.Beta2/ejb-remote) provides guidelines how to configure server and run ejb remote calls from client to server.

The text in README misses two points

• the server has to be setup with user/password credentials for the client may connect to it (otherwise the invocation failse). There is such information in the text but at the end of the guide and not at the place before the server is started (which is the correct location for it)
• there is not mentioned that's possible to run the client code without `mvn exec:exec` as the maven assembly plugin is configured in `pom.xml`. The text should contain a note how to run the assembly plugin and how then execute the client code.