add instructions to copy jetty.xml to example/conf to access web demos

[gurpartap0306]

Summary

This PR addresses a configuration issue that caused the demo to fail during startup due to an XML parsing error in jetty.xml.

Issue Fixed

Before this change, starting the demo threw the following error:

ERROR | Failed to load: file [/Users/user/workspace/activemq-brokers/apache-activemq-6.1.6/examples/conf/activemq-demo.xml], reason: IOException parsing XML document from file [/Users/user/workspace/activemq-brokers/apache-activemq-6.1.6/examples/conf/jetty.xml]

This was caused by the application not being able to resolve jetty.xml from the filesystem path. By updating the reference to use the classpath and ensuring the correct path is included, this issue is now resolved.

Added instructions to copy jetty.xml to example/conf to access web demos that fixes the issue.

[jbonofre]

I don't think we should add conf in classpath.

The default activemq.xml using related path (not classpath). Demo can do the same.

[gurpartap0306]

Thanks for the feedback! Initially, we used a relative path like <import resource="jetty.xml" />, which worked during testing because the test setup moved the demo files from example/conf to conf. However, this caused the DemoWebApp to fail at runtime since jetty.xml doesn't exist in example/conf.

To resolve this, I added conf to the test classpath to align it with the runtime environment. I did not modify the runtime classpath, keeping the production setup unchanged.

Other option is to add copy of jetty.xml in example/conf and use relative path. Let me know if you'd prefer this approach.

[jbonofre]

@gurpartap0306 yeah, I would prefer to copy (or document the copy) jetty.xml in example/conf. I don't want to add conf in the classpath (as it can be problematic for security, side effect, etc).

[gurpartap0306]

Thanks for the clarification. That makes sense. I'll update the PR with documentation to copy jetty.xml in example/conf.