Store_migration.MakeFunctor to create and register a migration.
module S_from : Store_sig.Smodule S_dest : Store_sig.Smodule Actions :
MIGRATION_ACTIONS
with type from_store := Mavryk_layer2_store.Store_sigs.ro S_from.t
and type dest_store := Mavryk_layer2_store.Store_sigs.rw S_dest.tval migrate :
Metadata.t ->
storage_dir:string ->
index_buffer_size:int ->
unit Mavryk_base.TzPervasives.tzresult Lwt.tMigration function for the store located in storage_dir.