OpenAPI: Iterate over models in SchemasStream

Use originally intended iterative approach to get next chunk of paths (for one model) in SchemasStream. The way that we will have:

toComponents(iterator.next(), isForSingleModule)
...
private static Deque<SchemaEntity> toComponents(final Module module, final boolean isForSingleModule) 

This will restore original draft idea presented in https://git.opendaylight.org/gerrit/c/netconf/+/108258 and possibly saves even more memory as we did for NETCONF-938. After work is done check performance with 2GiB heap space and 6 cores as is described in NETCONF-1234.