Add agent endpoint info to API response to /issuer

[esune]

A user-facing front-end consuming ToB APIs may need to direct an HTTP request directly to an agent: an example of this is dFlow when performing the request to obtain the dependencies for the desired credential.

There are two ways to obtain this information:

1. querying the Indy Ledger using the agent's did
2. receiving the information in the response to the /issuer API endpoint on ToB

Since ToB is already exposing a lot of the agent information, it makes sense to add this piece to the API response as well.

TODOs (in tob-api):

• obtain endpoint information from the Ledger when retrieving the rest of the agent information
• add endpoint information to the serialized API response to /issuer

[esune]

This PR in von-x enables CORS requests addressed to the agents, so that a webapp will be able to obtain data from them without having to go through a proxy.

This PR in ToB adds the new endpoint field to the /issuer API endpoint response.

[esune]

This is complete, however the bcreg agent will still need to be used as a proxy until Play With Docker can enable HTTPS.