Implement ParticipantContextManagementAPI

[paullatzelsperger]

add ParticipantContext Management API (using the ParticipantService) that requires "super-user" access. Specifically, the following operations should be supported:

• POST /participants: body contains a ParticipantManifest
• GET /participants?id=<PARTICIPANTID> returns ParticipantContext object. if no id is specified, returns all participant contexts.
• POST /participants/{participantId}/token: regenerates and returns the API token for the participant
• POST /participants/{participantId}/state?active=true activates or deactivates a participant context, emitting an event. Transitioning within the same state is a NOOP. On activation, the DID gets published, on deactivation it gets un-published.
• DELETE /participants/{participantId} deletes a participant, cascading down to all related entities:
  • VerifiableCredentials
  • DID documents (unpublish, then delete DidResource)
  • KeyPair resources

Minimal structure for a ParticipantManifest:

{
  "serviceEndpoints" : [ 
  {
    "id": ...,
    "type": ...,
    "serviceEndpoint":...
  }
  ],
  "isActive": true|false,
  "autoPublish": true|false,
  "participantId": "bpn, etc.",
  "key":{ ... } //check #212 
	
}

Depends on #212, #215