Offering, selecting, and/or changing the envelope protocol version

The aries-framework-go team (@Baha-sk and @llorllale) has been working on the implementation of a new encryption envelope format [RFC 0334](https://github.com/hyperledger/aries-rfcs/tree/master/features/0334-jwe-envelope), as has the DIDComm group at DIF. While it would be best if those efforts merge, it raises a separate question:

> How will the community enable collaboratively evolving the encryption envelope version to use for connections?

Just as the OOB invitation makes it possible for agents to offer new versions of a connection establishment protocol, we will need a way for agents to offer and select the envelope protocol to use for a new connection, as well as a way to propose and accept a change to the envelope protocol in use for a long lasting connection.

Should we extend the OOB now to enable that? Do we need to think about adding a connection management protocol along the lines of the proposed sync-connection protocol ([RFC 0030](https://github.com/hyperledger/aries-rfcs/tree/master/features/0030-sync-connection)) but extended to cover this requirement? Note that while 0030 is focused on peer:dids, this aspect of connection management needs to cover other than did:peer DID methods.