[Perf]Potential Speedup by returning a ref instead of a clone when asking for the RootDSE

We can speedup the server if we don't clone the rootDSE when we simply need to check for the presence of some values, like in protocol-ldap/src/main/java/org/apache/directory/server/ldap/handlers/SearchHandler.java :

DirectoryService ds = session.getCoreSession().getDirectoryService();
PartitionNexus nexus = ds.getPartitionNexus();
Value<?> subschemaSubentry = nexus.getRootDSE( null ).get( SchemaConstants.SUBSCHEMA_SUBENTRY_AT ).get();
LdapDN subschemaSubentryDn = new LdapDN( ( String ) ( subschemaSubentry.get() ) );
subschemaSubentryDn.normalize( ds.getRegistries().getAttributeTypeRegistry().getNormalizerMapping() );
String subschemaSubentryDnNorm = subschemaSubentryDn.getNormName();

when we call the getRootDSE method, we get back a clone, and this is done once per search. We just need the SubschemaSubentry attribute's value here, and we won't change it.

We could create a getRootDseRef() which returns a reference to the rootDSE object.