feat: Ability to unrelate private documents from actors (#3099)

## Relevant issue(s)
Resolves #2906 

## Description
Follow-up to #2907, the
ability to delete a relationship (in order to revoke access from an
identity).

## CLI Demo
The following revokes the target actors 'relational' access to the
private doc (can't read anymore):

```bash
defradb client acp relationship delete \
--collection Users \
--docID bae-ff3ceb1c-b5c0-5e86-a024-dd1b16a4261c \
--relation reader \
--actor did:key:z7r8os2G88XXBNBTLj3kFR5rzUJ4VAesbX7PgsA68ak9B5RYcXF5EZEmjRzzinZndPSSwujXb4XKHG6vmKEFG6ZfsfcQn \
--identity e3b722906ee4e56368f581cd8b18ab0f48af1ea53e635e3f7b8acd076676f6ac
```

Result:
```json
{
  "RecordFound": true // <-------------- Indicates a relationship was found and deleted
}
```


## How has this been tested?
 CI + Integration Tests + Unit Tests

acp/README.md

@@ -631,6 +631,70 @@ Result:
 Error: document not found or not authorized to access
 ```
 
+### Revoking Access To Private Documents
+
+To revoke access to a document for an actor, we must delete the relationship between the
+actor and the document. Inorder to delete the relationship we require all of the following:
+
+1) Target DocID: The docID of the document we want to delete a relationship for.
+2) Collection Name: The name of the collection that has the Target DocID.
+3) Relation Name: The type of relation (name must be defined within the linked policy on collection).
+4) Target Identity: The identity of the actor the relationship is being deleted for.
+5) Requesting Identity: The identity of the actor that is making the request.
+
+Notes:
+  - ACP must be available (i.e. ACP can not be disabled).
+  - The target document must be registered with ACP already (policy & resource specified).
+  - The requesting identity MUST either be the owner OR the manager (manages the relation) of the resource.
+  - If the relationship record was not found, then it will be a no-op.
+
+Consider the same policy and added relationship from the previous example in the section above where we learnt
+how to share the document with other actors. 
+
+We made the document accessible to an actor by adding a relationship:
+```sh
+defradb client acp relationship add \
+--collection Users \
+--docID bae-ff3ceb1c-b5c0-5e86-a024-dd1b16a4261c \
+--relation reader \
+--actor did:key:z7r8os2G88XXBNBTLj3kFR5rzUJ4VAesbX7PgsA68ak9B5RYcXF5EZEmjRzzinZndPSSwujXb4XKHG6vmKEFG6ZfsfcQn \
+--identity e3b722906ee4e56368f581cd8b18ab0f48af1ea53e635e3f7b8acd076676f6ac
+```
+
+Result:
+```json
+{
+  "ExistedAlready": false
+}
+```
+
+Similarly, inorder to revoke access to a document we have the following command to delete the relationship:
+```sh
+defradb client acp relationship delete \
+--collection Users \
+--docID bae-ff3ceb1c-b5c0-5e86-a024-dd1b16a4261c \
+--relation reader \
+--actor did:key:z7r8os2G88XXBNBTLj3kFR5rzUJ4VAesbX7PgsA68ak9B5RYcXF5EZEmjRzzinZndPSSwujXb4XKHG6vmKEFG6ZfsfcQn \
+--identity e3b722906ee4e56368f581cd8b18ab0f48af1ea53e635e3f7b8acd076676f6ac
+```
+
+Result:
+```json
+{
+  "RecordFound": true
+}
+```
+
+**Note: If the same relationship is deleted again (or a record for a relationship does not exist) then the `RecordFound`
+would be false, indicating no-op**
+
+Now the other actor can no longer read:
+```sh
+defradb client collection docIDs --identity 4d092126012ebaf56161716018a71630d99443d9d5217e9d8502bb5c5456f2c5
+```
+
+**Result is empty from the above command**
+
 ## DAC Usage HTTP:
 
 ### Authentication

acp/acp.go

@@ -115,6 +115,23 @@ type ACP interface {
 		targetActor string,
 	) (bool, error)
 
+	// DeleteDocActorRelationship deletes a relationship between document and the target actor.
+	//
+	// If failure occurs, the result will return an error. Upon success the boolean value will
+	// be true if the relationship record was found, and deleted. Upon success the boolean
+	// value will be false if the relationship record was not found (no-op).
+	//
+	// Note: The request actor must either be the owner or manager of the document.
+	DeleteDocActorRelationship(
+		ctx context.Context,
+		policyID string,
+		resourceName string,
+		docID string,
+		relation string,
+		requestActor identity.Identity,
+		targetActor string,
+	) (bool, error)
+
 	// SupportsP2P returns true if the implementation supports ACP across a peer network.
 	SupportsP2P() bool
 }

acp/acp_local.go

@@ -267,3 +267,33 @@ func (l *ACPLocal) AddActorRelationship(
 
 	return setRelationshipResponse.RecordExisted, nil
 }
+
+func (l *ACPLocal) DeleteActorRelationship(
+	ctx context.Context,
+	policyID string,
+	resourceName string,
+	objectID string,
+	relation string,
+	requester identity.Identity,
+	targetActor string,
+	creationTime *protoTypes.Timestamp,
+) (bool, error) {
+	principal, err := auth.NewDIDPrincipal(requester.DID)
+	if err != nil {
+		return false, newErrInvalidActorID(err, requester.DID)
+	}
+
+	ctx = auth.InjectPrincipal(ctx, principal)
+
+	deleteRelationshipRequest := types.DeleteRelationshipRequest{
+		PolicyId:     policyID,
+		Relationship: types.NewActorRelationship(resourceName, objectID, relation, targetActor),
+	}
+
+	deleteRelationshipResponse, err := l.engine.DeleteRelationship(ctx, &deleteRelationshipRequest)
+	if err != nil {
+		return false, err
+	}
+
+	return deleteRelationshipResponse.RecordFound, nil
+}