update startCompute action

[MBadea17]

Action startCompute is called by /initiateCompute endpoint of Ocean Node to check the access credentials of a specific consumer to a specific service of an asset. Currently, the action startCompute expects in the policyServer object information related to a single service, as shown below:

{
  "action": "startCompute",
  "serviceId": "ff294c2e2c7d01bd5f9701abc117737917bb1f91044ba6b2d0903fc806db0d65",
  "consumerAddress": "0xd727fb9be39fa019d7c02fea19e54d688da3a662",
  "policyServer": {
    "successRedirectUri": "",
    "sessionId": "",
    "errorRedirectUri": "",
    "responseRedirectUri": "",
    "presentationDefinitionUri": ""
  },
  "ddo": {...}
}

However, /initiateCompute will pass in the policyServer object information about all services used in the C2D job. The structure of the policyServer object passed by /initializeCompute will be:

{
    "policyServer": [
        { "documentId": "did1",
          "serviceId": "service1",    
          "successRedirectUri": "",
          "sessionId": "",
          "errorRedirectUri": "",
          "responseRedirectUri": "",
          "presentationDefinitionUri": ""
        },
         { "documentId": "did2",
          "serviceId": "service2",    
          "successRedirectUri": "",
          "sessionId": "",
          "errorRedirectUri": "",
          "responseRedirectUri": "",
          "presentationDefinitionUri": ""
        },
        ...
    ]
}

Therefore, the startCompute action needs to be updated as follows:

1. read the documentId parameter from the request body. Here's the list of parameters sent by the node for the startCompute action.
   The request body will look like this:

{
  "action": "startCompute",
  "documentId": "did:ope:...."
  "serviceId": "ff294c2e2c7d01bd5f9701abc117737917bb1f91044ba6b2d0903fc806db0d65",
  "consumerAddress": "0xd727fb9be39fa019d7c02fea19e54d688da3a662",
  "policyServer": {
    "successRedirectUri": "",
    "sessionId": "",
    "errorRedirectUri": "",
    "responseRedirectUri": "",
    "presentationDefinitionUri": ""
  },
  "ddo": {...}
}

2. from the list passed in the policyServer object, find the item corresponding to the documentId and serviceId passed in the request body;
3. retrieve the data from this item;
4. perform the existing credentials verification process using the retrieved data.