EcdsaSecp256k1Signature2019 matchProof should support relative paths id of verificationMethod

[lemoustachiste]

This block https://github.com/hellobloom/ssi-sdk/blob/main/packages/ecdsa-secp256k1-signature-2019/src/index.ts#L194-L197 expects to match the key id and the verificationMethod id.

However, as per this discussion: decentralized-identity/ion#285, relative paths in verificationMethod of a DID document are a valid format to reference a key id.

When running verification with EcdsaSecp256k1Signature2019 in the case of a relative path definition in the DID document, the validation fails with:

Did not verify any proofs; insufficient proofs matched the acceptable suite(s) and required purpose(s).

Because the above check does not match the relative path.

I don't mind opening a PR if that's easier on you, but there needs to be a way to also check that the controller is valid, and I'm not sure if we've got access to that.

[djvs]

Sorry for delay. Please do PR and I can review.