automatically index proxied artifacts

currently the proxied artifacts will only be indexed when the indexer is next run.

We should automatically index them, but some care needs to be taken:

• make sure the indexer is thread safe and won't regularly fail with a failed lock
• find the best way to hook this up by design (need to separate proxied artifacts from proxied files as this is internal to the proxy code, and don't want the indexer into the proxy code but rather in the core).