Support individual certificate for a single artifact, the certificate can be separated or included in the artifact signature file.
From the ETSI GS NFV-SOL 004 V2.6.1, item 5.4:

One certificate per signed artifact:
Either a certificate file with extension .cert is included as a sibling of the signed artifact file, i.e. placed in the
same folder as the signed artifact and having the same name (different extension) or the certificate is included
in the signature file, provided that the signature format allows for it. This alternative allows to have different
certificates per different artifacts, which may be needed e.g. if artifacts contained in the package are signed by
3rd party providers.

Either allow to one of the following options, not both together:

• One certificate per signed artifact;
• One single certificate for all signed artifacts.

From the ETSI GS NFV-SOL 004 V2.6.1, item 5.4:

A certificate shall also be included in the VNF package as per one of the two following alternatives:
• One certificate per signed artifact:
[...]
• One single certificate for all signed artifacts:
[...]