feat: Add Photon indexer

[vadorovsky]

Add a new, tiny implementation of Photon client, which can be used in third-party program tests.

Differences between the old and new implementation:

• Lack of dependency on Light Protocol program crates.
• Support of:
  • get_compressed_accounts_by_owner - which returns the whole accounts, not just hashes
  • get_validity_proof - which is essential for getting proofs for new compressed accounts