add update_master_signatures

src/api_sig.ml

@@ -48,6 +48,7 @@ end) : sig
   (* Ok () on verification success *)
   val verify : key:Crypto.EddsaPublicKey.t -> t -> r -> (unit, string) result
   val jsont : t Jsont.t
+  val caqti : t Caqti_type.t
 end = struct
   open Crypto
 
@@ -64,6 +65,14 @@ end = struct
     | true -> Ok ()
 
   let jsont = EddsaSignature.jsont
+
+  let caqti : EddsaSignature.t Caqti_type.t =
+    let open Caqti_type in
+    let open EddsaSignature in
+    custom
+      ~encode:(fun v -> Ok (to_octets v))
+      ~decode:(fun s -> Ok (of_octets s))
+      octets
 end
 
 module DenominationKeyAnnouncementPS = struct