Refactor entitlement IT test to allow dynamic policy (#120443) (#120666)

This commit combines the different entitlement test plugins used for
integration tests into a single plugin. When installing the plugin in
the integ test cluster, the entitlement policy and plugin properties are
adjusted to test the desired combination of settings. This allows the
plugin policy to be dynamically generated by each test, rather than rely
on a static policy.

Author: rjernst

libs/entitlement/qa/build.gradle

@@ -12,9 +12,6 @@ apply plugin: 'elasticsearch.internal-java-rest-test'
 apply plugin: 'elasticsearch.internal-test-artifact'
 
 dependencies {
-  javaRestTestImplementation project(':libs:entitlement:qa:common')
-  clusterModules project(':libs:entitlement:qa:entitlement-allowed')
-  clusterModules project(':libs:entitlement:qa:entitlement-allowed-nonmodular')
-  clusterPlugins project(':libs:entitlement:qa:entitlement-denied')
-  clusterPlugins project(':libs:entitlement:qa:entitlement-denied-nonmodular')
+  javaRestTestImplementation project(':libs:entitlement:qa:test-plugin')
+  clusterModules project(':libs:entitlement:qa:test-plugin')
 }