Cloud: Fix stack wake-up function

Closes #1725

In #1545, the stack readiness check was improved by calling the `/api/health` endpoint instead of just the stack URL
While this does provide a better indication that the instance is up and running, the `/api/health` subpath does not trigger Grafana Cloud's stack wake-up
With this PR, we'll call both the stack's base URL and its health endpoint

Author: julienduchesne

internal/resources/cloud/resource_cloud_stack.go

@@ -445,25 +445,37 @@ func waitForStackReadiness(ctx context.Context, timeout time.Duration, stackURL
 		return diag.FromErr(joinErr)
 	}
 	err := retry.RetryContext(ctx, timeout, func() *retry.RetryError {
-		req, err := http.NewRequestWithContext(ctx, http.MethodGet, healthURL, nil)
+		// Query the instance URL directly. This makes the stack wake-up if it has been paused.
+		// The health endpoint is helpful to check that the stack is ready, but it doesn't wake up the stack.
+		stackReq, err := http.NewRequestWithContext(ctx, http.MethodGet, stackURL, nil)
 		if err != nil {
 			return retry.NonRetryableError(err)
 		}
-		resp, err := http.DefaultClient.Do(req)
+		stackResp, err := http.DefaultClient.Do(stackReq)
 		if err != nil {
 			return retry.RetryableError(err)
 		}
-		defer resp.Body.Close()
-		if resp.StatusCode != 200 {
+		defer stackResp.Body.Close()
+
+		healthReq, err := http.NewRequestWithContext(ctx, http.MethodGet, healthURL, nil)
+		if err != nil {
+			return retry.NonRetryableError(err)
+		}
+		healthResp, err := http.DefaultClient.Do(healthReq)
+		if err != nil {
+			return retry.RetryableError(err)
+		}
+		defer healthResp.Body.Close()
+		if healthResp.StatusCode != 200 {
 			buf := new(bytes.Buffer)
 			body := ""
-			_, err = buf.ReadFrom(resp.Body)
+			_, err = buf.ReadFrom(healthResp.Body)
 			if err != nil {
 				body = "unable to read response body, error: " + err.Error()
 			} else {
 				body = buf.String()
 			}
-			return retry.RetryableError(fmt.Errorf("stack was not ready in %s. Status code: %d, Body: %s", timeout, resp.StatusCode, body))
+			return retry.RetryableError(fmt.Errorf("stack was not ready in %s. Status code: %d, Body: %s", timeout, healthResp.StatusCode, body))
 		}
 
 		return nil