Keystore overhaul (#13615)

* Remove 'supported_keys' 'sign_with_any' and 'sign_with_all' from keystore trait

* Remove the aync keystore

* Renaming:
- SyncCryptoStore -> Keystore
- SyncCryptoStorePtr -> KeystorePtr
- KeyStore -> MemoryKeystore

* Fix authority discovery worker and tests

* Rename 'insert_unknown' to 'insert'

* Remove leftover