Issuer Trust List should not be restricted to a DIF design

[timcappalli]

A verifier-controlled DIF Credential Trust Establishment document

This should be generalized to cover the general trust list concept

[dan-proof]

I removed altogether, and given we have another party who wants to specify an allowed list type within the cred requirements DCQL area for trusted authorities, I think we should consider this issue holistically. That other party has a PR in for their list type, so having a general stance/direction would be helpful.