In filemode emit the hash which uniquely identifies a given Signed Object

In filemode emit the hash which uniquely identifies a given Signed Object

RPKI Signed Objects are not malleable; this means the SHA256 digest
of an input file containing a signed object is a very stable identifier
to associate with the decoded (validated) output shown in filemode.

The SHA256 in hash_id is base64 encoded (just like hashes on manifest listings).

OK tb@