Communicate with network indexers for content routing using reader privacy with double hashing

## Done Criteria
Content routing calls like ``findProviders`` to Network Indexers like cid.contact preserve reader privacy with double hashing. Using double hashing is the implicit default.

## Why Important
Move IPFS' privacy story forward so that centralized endpoints like network indexers are not even able to know "who is contacting what". This is about getting to a system where we don't have to trust network indexers to respect a client's privacy.

## Notes
1. There is a lot still be designed here. This is the Kubo tracking issue so we can link to other work.
2. This is a followup to https://github.com/ipfs/kubo/issues/9454
3. Related docs:
- https://www.notion.so/pl-strflt/Double-Hashing-for-Privacy-ff44e3156ce040579289996fec9af609
- https://protocollabs.notion.site/Double-Hashing-and-Indexers-abe2e24aa5974f5ebd7fc42a17f1bd05
- https://github.com/ipni/specs/pull/5