WIP: Run activemq container as non root

[alxgomz]

This PR is a proposal to address https://issues.apache.org/jira/browse/AMQ-9588

It's trying to keep the same behavior of the container and essentially:

• Leverage properties lookup where possible so configuration can be done using env vars rather than sed (unfortunatelly properties lookup do not work for the anonymousAccessAllowed param of simpleAuthenticationPluginso I left it on by default to mimic to previous behavior)
• Allow building images with non default credentials
• Switch build process to multistage build to allow more robust installation/configuration of the activemq distrib
• Fix web console auth for ActiveMQ 5.x
• Create a non privileged user to run to service
• Update doc

[mattrpav]

1. Leaving JMX enabled, but optionally exposing the port is a simple approach to remove a lot of scaffolding.

2. Why is JAAS not the default just like the dist?

[alxgomz]

Hi @mattrpav thanks for taking the time to review.

1. Toggling JMX on and off is actually the very lightweight part of this PR. To be honest I have introduced it because I wanted to keep a similar behaviour to what pre-existed. But I would personally remove it completely given, a) JMX is such a pain in most docker environments and really not well suited to NAT networks in general and b) the authentication as it is set right now simply doesn't work: even if user and password are set one can still login anonymously as soon as the createConnector param is set t io true (btw, the doc seems to mention the jmx authenticated access should be set up using java OPTS and with the ManagementContext turned off but I could not get it to work). And c) I remember reading theere's a jolokia endpoint available somewhere that would deliver just the same data in a more friendly fashion. But I decided I would not make this kind more disruptive approach.

2. The reason I did not used JaaS to configure web user s because I'm working with ActiveMQ 5.18 which do not seem to have the appropriate classes available and throws this error when trying to do use it:

ERROR | Failed to load: class path resource [activemq.xml], reason: Failed to load type: org.eclipse.jetty.jaas.JAASLoginService. Reason: java.lang.Cl
assNotFoundException: org.eclipse.jetty.jaas.JAASLoginService; nested exception is java.lang.ClassNotFoundException: org.eclipse.jetty.jaas.JAASLoginS
ervice                                                                                                                                                
org.springframework.beans.factory.BeanDefinitionStoreException: Failed to load type: org.eclipse.jetty.jaas.JAASLoginService. Reason: java.lang.ClassN
otFoundException: org.eclipse.jetty.jaas.JAASLoginService; nested exception is java.lang.ClassNotFoundException: org.eclipse.jetty.jaas.JAASLoginServi
ce

Taking a look at the 5.x distribution I saw the default user was using jetty-realm properties file which was only available in 5.x dists so I chose to rely on the presence of this file to decide wether I would set the default web user

[alxgomz]

@mattrpav as you renamed this PR title I was wondering whether you were expecting more work from me or are yo planning to take over from here?