Remaining work on DIDComm module

[genaris]

Some ideas we got from #2127 that would be good to check before official 0.6.0 release:

• Fix build (core dependency on didcomm) (fix: exclude test types from core #2167 )
• agent.didcomm possible (nesting is getting quite large)
  nest didcomm modules under agent.didcomm, also because agent.credentials / agent.modules.credentials is misleading, since it's didcomm specific. I think registerin
• Adopting the conenctions / oob modules into the didcomm module by default, and you can configure it in the didcomm module config again. I think this simplifies setup.
• Registering custom didcomm protocols on the didcomm module rather than the agent? This may solve some of the initialization and feature registry issues. We can create a DidcommModule interface that has special feature registry etc.
• Rename modules to have DIDcomm prefix (DidCommConnectionsModule, DidCommMessageHandlerRegistry). This will help with identifiying for what feature a class is
• Add inbound / outbound transports to the config? I always found it a bit weird you can't just add this to the didcomm config
• Check Tenants dependency on DIDComm (connectionImageUrl, Routing, etc.)
• Label is still part of Agentconfig because it is used by Tenants
• Remove MessageSender dependency on MessagePickupRepository injection symbol. Maybe this can be solved with events, so base DIDComm and MessagePickup modules are decoupled (feat: remove MessagePickupRepository injection symbol #2168)