use did:key for peer IDs

[chunningham]

Description

Currently peers are represented in delegations by URIs of the form peer:<PEER-ID>, which is neither a proper URI or a DID. This PR adds a way to get a did:key DID of a peer. At the moment this is mostly an aesthetic change as we don't use peer IDs, but it's a change we should make before we start using the Peers keys to sign things

Type

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Diligence Checklist

(Please delete options that are not relevant)

• This change requires a documentation update
• I have included unit tests
• I have updated and/or included new integration tests
• I have updated and/or included new end-to-end tests
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules