Use versionless alias to ES rest client codebase (elastic/x-pack-elasticsearch#2441)

This is the xpack side of
https://github.com/elastic/elasticsearch/pull/26521

Original commit: elastic/x-pack-elasticsearch@b650e9e433

plugin/src/main/plugin-metadata/plugin-security.policy

@@ -32,7 +32,7 @@ grant {
   permission java.io.FilePermission "\\\\.\\pipe\\*", "read,write";
 };
 
-grant codeBase "${codebase.elasticsearch-rest-client-7.0.0-alpha1-SNAPSHOT.jar}" {
+grant codeBase "${codebase.elasticsearch-rest-client}" {
   // rest client uses system properties which gets the default proxy
   permission java.net.NetPermission "getProxySelector";
 };