[Feature] Add did:web issuer support for ldp issuance/verification endpoints

[PatStLouis]

The newly added endpoints to issue/verify json-ld vc's make use of the issuer field to find the signing key, limiting the issuance to did:key. In the event I have registered a did:key in my wallet and chose to host the verification method through a did:web identifier, I should be able to use this as my issuer id.

I would like to see a way for the agent to resolver a did:web document and fetch the verification keys from said document to decide which key to sign the payload with. Since acapy already supports a resolver endpoint this can enable such a feature.

The same would be made for the verification, I would like to refer to a did:web verification key which can be resolved to verify the payload.

The endpoints in question are /vc/ldp/issue and /vc/ldp/verify