[DIDComm Connector] Basic Functionality to integrate with PCM Cloud - Part 1

DIDComm Connector Common Service must implement functionality ready to be used by following PCM consumers:

• eclipse/xfsc/personal-credential-manager-cloud&14
• eclipse/xfsc/personal-credential-manager-cloud/service-epics#76
• eclipse/xfsc/personal-credential-manager-cloud&25
• (indirect) eclipse/xfsc/personal-credential-manager-cloud&22
• (partially, only DIDComm aspects) eclipse/xfsc/personal-credential-manager-cloud&26
• (consumed by Connection Manager for cryptography - also see: https://gitlab.eclipse.org/eclipse/xfsc/libraries/crypto/engine) eclipse/xfsc/personal-credential-manager-cloud&27