Implement SignerRegistrationStore providers & adapter

Author: jpraynaud

mithril-aggregator/src/database/provider/mod.rs

@@ -2,9 +2,11 @@
 mod certificate;
 mod epoch_setting;
 mod open_message;
+mod signer_registration;
 mod stake_pool;
 
 pub use certificate::*;
 pub use epoch_setting::*;
 pub use open_message::*;
+pub use signer_registration::*;
 pub use stake_pool::*;