Fix deprecated Kibana APIs (#2236)

Fixed API to get the list of Elastic Agents available and the API to
reassign one policy to an Elastic Agent.
Fixed policy name to be used in Kubernetes for 9.x stack

internal/agentdeployer/kubernetes.go

@@ -221,11 +221,12 @@ func readCACertBase64(profile *profile.Profile) (string, error) {
 	return base64.StdEncoding.EncodeToString(d), nil
 }
 
-// getTokenPolicyName function returns the policy name for the 8.x Elastic stack. The agent's policy
-// is predefined in the Kibana configuration file. The logic is not present in older stacks.
+// getTokenPolicyName function returns the policy name for the >= 8.x Elastic stacks. The agent's policy
+// is predefined in the Kibana configuration file. The logic is not present in older stacks and it uses
+// the default policy in Kibana (empty string).
 func getTokenPolicyName(stackVersion, policyName string) string {
-	if strings.HasPrefix(stackVersion, "8.") {
-		return policyName
+	if strings.HasPrefix(stackVersion, "7.") {
+		return ""
 	}
-	return ""
+	return policyName
 }

internal/kibana/agents.go

@@ -59,22 +59,36 @@ func (c *Client) ListAgents(ctx context.Context) ([]Agent, error) {
 	}
 
 	var resp struct {
-		List []Agent `json:"list"`
+		List  []Agent `json:"list"`
+		Items []Agent `json:"items"`
 	}
 
 	if err := json.Unmarshal(respBody, &resp); err != nil {
 		return nil, fmt.Errorf("could not convert list agents (response) to JSON: %w", err)
 	}
 
-	return resp.List, nil
+	switch {
+	case c.semver.Major() < 9:
+		return resp.List, nil
+	default:
+		return resp.Items, nil
+	}
 }
 
 // AssignPolicyToAgent assigns the given Policy to the given Agent.
 func (c *Client) AssignPolicyToAgent(ctx context.Context, a Agent, p Policy) error {
 	reqBody := `{ "policy_id": "` + p.ID + `" }`
-
 	path := fmt.Sprintf("%s/agents/%s/reassign", FleetAPI, a.ID)
-	statusCode, respBody, err := c.put(ctx, path, []byte(reqBody))
+
+	var statusCode int
+	var err error
+	var respBody []byte
+	switch {
+	case c.semver.Major() < 9:
+		statusCode, respBody, err = c.put(ctx, path, []byte(reqBody))
+	default:
+		statusCode, respBody, err = c.post(ctx, path, []byte(reqBody))
+	}
 	if err != nil {
 		return fmt.Errorf("could not assign policy to agent: %w", err)
 	}