Add support for Bls12381G2 keys in did-provider-key

The existing implementation for did-provider-key only allows creating identifiers for 'Ed25519'. It is not possible to extend it to support other key types such as 'Bls12381G2'.

The only supported key type is hardcoded here. https://github.com/uport-project/veramo/blob/next/packages/did-provider-key/src/key-did-provider.ts#L28

It would be ideal if we can pass the key type as an option for this implementation and also override how the specific portion for the key identifier is generated. For instance, Bls12381G2 uses a different prefix. See here, https://github.com/pcibraro/veramo/blob/next/packages/did-provider-key-bbs/src/key-did-provider.ts#L32

Also, the DIDResolver implementation in the resolver.ts file is hardcoded with a few supported prefixes (for key types) https://github.com/uport-project/veramo/blob/next/packages/did-provider-key/src/resolver.ts#L6. It would be great if that can be extended to support other prefixes like the one used by Bls12381G2.