Many software packages do not support 128 bits arcs in OIDs (see
https://misc.daniel-marschall.de/asn.1/oid_facts.html#chap4), use a
registered OID instead.

Certificates emitted using the legacy OID are migrated to the new OID on
renewal.

Mix of work by Vincent Pelletier <vincent@nexedi.com> and
Thomas Gambier <thomas.gambier@nexedi.com> finished by
Lukasz Nowak <luke@nexedi.com>