☂️: Self-transparent, COSE-only ledgers

[maxtropets]

Completion of this umbrella brings us to

• COSE-only signed ledgers with self-transparency capabilities
• fast and clean receipt generation/verification

Self-transparency breakdown (somewhat in order)

• C++ API to verify COSE receipts (COSE receipt verification in C++ API  #7494)
• C++ API to verify self-signing (current identity only) (COSE receipt verification in C++ API  #7494)
• Preload previous service identities on startup (Prefetch COSE endorsements of previous identities #7518)
• Better C++ API to verify self-signing (including any previous identity)
• JS wrappers for self-signing checking and receipt verification (maybe a single all-in-one call, to be defined)

COSE-only breakdown (somewhat in order too)

• COSE-only receipt format
• New snapshot format (with new receipt)
  • to be backported: consuming new snapshots
• COSE-only signature config (make sure it's one-way)
  • to be backported: consuming COSE-only signed entries

Other important things

• Snapshot format change, to include both COSE receipts and previous service identities endorsement chain
• COSE receipts endpoint
• Make COSE back-endorsement chain optional
• Check Create a dedicated endpoint for COSE service identity endorsement verification #6560
• Maybe blocking-commit dup related, but make sure to get rid of retrying for historical queries