add suppression list for outgoing dmarc and tls reports

for reporting addresses that cause DSNs to be returned. that just adds noise.
the admin can add/remove/extend addresses through the webadmin.

in the future, we could send reports with a smtp mail from of
"postmaster+<signed-encoded-recipient>@...", and add the reporting recipient
on the suppression list automatically when a DSN comes in on that address, but
for now this will probably do.

tlsrptdb/db.go

@@ -17,7 +17,7 @@ var (
 	mutex         sync.Mutex
 
 	// Accessed directly by tlsrptsend.
-	ResultDBTypes = []any{TLSResult{}}
+	ResultDBTypes = []any{TLSResult{}, TLSRPTSuppressAddress{}}
 	ResultDB      *bstore.DB
 )