Add easy way to discover protocol version for issue credential and present proof

[TimoGlastra]

In the current API designs, when issuing a credential or requesting a proof you need to pass in a protocolVersion parameter. This specifies whether you want to use version 1 or version 2 of the protocol.

We should add an easy method to the CredentialModule or the DiscoveryModule that returns the version of a protocol for a specific connection. This to make the handling of multiple protocols versions as easy as possible. This is only needed when initiating a protocol, as from then we can infer the protocol version from the messages.

• Do a issue-credential feature discover query with an * for the version.
• Pick the latest version that we support (2.0 preferred, fallback 1.0)

agent.credentials.getProtocolVersion(connectionId: string): Promise<IssueCredentialProtocolVersion>