fix(activemq): use <users>/<authenticationUser> child elements (XSD lies about String-typed attributes)

[natechadwick-intsof]

Summary

The activemq.xsd advertises userPasswords and userGroups as
xs:string attributes on <simpleAuthenticationPlugin>, but the
actual org.apache.activemq.security.SimpleAuthenticationPlugin
class in 5.16.8 has:

public void setUserPasswords(java.util.Map<java.lang.String, java.lang.String>);
public void setUserGroups(java.util.Map<java.lang.String, java.util.Set<java.security.Principal>>);

— i.e., the setters take Map, not String. There is no custom
property editor registered, so Spring's BeanWrapper rejects the
activemq.xml bean init with:

ConversionNotSupportedException: Failed to convert property value of type
  'java.lang.String' to required type 'java.util.Map' for property
  'userGroups': no matching editors or conversion strategy found

The XSD's <xs:attribute name='userPasswords' type='xs:string'/> is a
documentation bug in activemq-spring-5.16.8.jar. PR #213 used the
attribute form because that's what the XSD implied; that form is
unusable. The correct way to express users in XBean is the
<users> / <authenticationUser> child-element pattern:

<simpleAuthenticationPlugin anonymousAccessAllowed="false">
    <users>
        <authenticationUser username="rhythmyx" password="rhythmyx" groups="users,admins"/>
    </users>
</simpleAuthenticationPlugin>

<authenticationUser> is the helper class
org.apache.activemq.security.AuthenticationUser (3-arg constructor
String username, String password, String groups plus the matching
setters), declared in the same activemq.xsd as a child of the
plugin's <users> element.

Plan

1. Replace the broken userPasswords="..." userGroups="..." attribute
   pair with a <users><authenticationUser .../></users> child
   element. Keep anonymousAccessAllowed="false".
2. The connection-factory changes from PR fix(activemq): add in-VM user credentials to simpleAuthenticationPlugin + ConnectionFactory #213 (perc-mq.xml,
   ear/WEB-INF/jetty-env.xml) are unchanged — they still work.
3. Branch bugfix/<this-issue>-activemq-users-child-element; commit,
   GPG-sign, push, open PR.

Verification

• python3 -c "import xml.etree.ElementTree as ET; ET.parse('activemq.xml')" — well-formed.
• xmllint --schema activemq.xsd activemq.xml --noout — exits 0.
• After deploy + restart:
  • grep -c "Failed to load: class path resource \[activemq.xml\]" .../server.log — 0
  • grep -c "User name \[null\] or password is invalid" .../server.log — 0
  • grep -c "Failed to convert property value" .../server.log — 0
  • JMS listeners reach steady state.

Co-Authored by Mavis Mavis-Code using MiniMax-M3 with agent mavis.

[natechadwick-intsof]

Closing as completed by PR #215. Using / child elements (XSD-lies fix).