namespace: relax HSM URI validation rules

dcache requires hsm type and hsm instance are provided.
Ignore all other rules as it's OPAQUE to us.

Ticket: #7192
Acked-by: Gerd Behrmann
Target: master, 2.7, 2,6
Require-book: no
Require-notes: no
Merge pull request #216 from kofemann/iss7192-2.6

namespace: relax HSM URI validation rules