Fixes SAML tests in testsuite

- adds dependency to saaj-impl in saml core public
- updates test apps' web.xml files to use jakarta namespaces
- small cleanup in main pom
- changes order of e-mail servers in testsuite pom to enforce usage of greenmail (changes order in Undertow's classpath)

Closes #16711

boms/pom.xml

@@ -22,6 +22,7 @@
         <groupId>org.jboss</groupId>
         <artifactId>jboss-parent</artifactId>
         <version>39</version>
+        <relativePath/>
     </parent>
 
     <groupId>org.keycloak.bom</groupId>