[Cloud Security] fix cloud formation pop-up flicker (#191136)

## Summary

Summarize your PR. If it involves visual changes include a screenshot or
gif.

If go to CSPM page and click save and continue, the Cloud Formation Pop
occasionally flickers and shows Fleet Server host error for one second.
This PR adds a boolean `isLoadingIntialRequest` for us to wait after
loading Fleet Server hosts before showing the errors.

[Quick Wins](elastic/security-team#10316)

Locally:

https://github.com/user-attachments/assets/bf393103-9d21-4ddf-96a9-8fc3e9626369

Serverless QA


https://github.com/user-attachments/assets/d1877a5a-97ba-4ce6-b87b-177656bdd004

x-pack/plugins/fleet/public/applications/fleet/sections/agent_policy/create_package_policy_page/single_page_layout/components/cloud_security_posture/post_install_cloud_formation_modal.tsx

@@ -44,7 +44,9 @@ export const PostInstallCloudFormationModal: React.FunctionComponent<{
   );
 
   const { agentPolicyWithPackagePolicies } = useAgentPolicyWithPackagePolicies(agentPolicy.id);
-  const { fleetServerHost } = useFleetServerHostsForPolicy(agentPolicyWithPackagePolicies);
+  const { fleetServerHost, isLoadingInitialRequest } = useFleetServerHostsForPolicy(
+    agentPolicyWithPackagePolicies
+  );
 
   const cloudFormationProps = getCloudFormationPropsFromPackagePolicy(packagePolicy);
 
@@ -67,7 +69,7 @@ export const PostInstallCloudFormationModal: React.FunctionComponent<{
 
       <EuiModalBody>
         <CloudFormationGuide awsAccountType={cloudFormationProps.awsAccountType} />
-        {error && isError && (
+        {error && isError && !isLoadingInitialRequest && (
           <>
             <EuiSpacer size="m" />
             <EuiCallOut title={error} color="danger" iconType="error" />