IATP: create extensible way to contribute trusted issuers

[paullatzelsperger]

WHAT

We have a check in the VP validation that asserts, that all VCs have been issued by an "accepted" issuer, i.e. one that the participant deems trustworthy.

WHY

We need an extensible way of defining that list, because over the lifetime of a dataspace, it is to be expected that more than one credential issuers emerge. As a first step we can have this a config value (comma-separated strings).

FURTHER NOTES

In the future, there could even be extensions, that load this list of allowed issuers from a trusted source.

This is closely related to eclipse-tractusx/tractusx-edc#814, but should indeed be implemented here.

IMPLEMENTATION PROPOSAL

add a AllowedIssuerRegistry, that contains a List<String> with the issuer IDs