DID resolver service

Add a DID resolver service to the workspace.

A possible option to start with can be: https://github.com/decentralized-identity/universal-resolver

A possible implementation of a client can be seen in the Aries Go Framework. This commit seems to add such client functionality: https://github.com/hyperledger/aries-framework-go/pull/117/commits/43a9ba2c9acd9f03dbb1f8b459ae538aeae97591