[Infra] Change order of the errors shown on Infra pages (elastic#200531)

Closes elastic#200190

## Summary

This PR fixes the issue with the errors shown on the metrics explorer
page - when the metrics indices can't be fetched we should show the
error returned and if there is no fetch error and a remote cluster
configured but no connection is possible we should show the remote
cluster error:

- Example with 504 error

![image](https://github.com/user-attachments/assets/65cd8226-8c81-4c64-b043-c9db5a93d3e0)

- Example with remote cluster error

![image](https://github.com/user-attachments/assets/e024a3f8-76e0-4ad7-8aa6-e35ad5c1112a)

## Testing
Couldn't find a way to reproduce this so I "faked" the API response to
be an error and checked several cases
- API returns an error, we should show the error:

https://github.com/user-attachments/assets/c1086b22-1ff5-4333-97a5-b3d1dca16afe

- API doesn't return an error but the remote cluster connection wasn't
possible, we should show the remote cluster error:

https://github.com/user-attachments/assets/151b3ae4-5ca1-4d54-bd58-2729db202cdb

- If no remote cluster is used/or a remote cluster is connected and the
API response is not returning an error the page should load correctly:

https://github.com/user-attachments/assets/f9ef1066-3dfd-4957-8b46-878bf58d2f1c
(cherry picked from commit 46d4c84)

# Conflicts:
#	x-pack/plugins/observability_solution/infra/public/pages/metrics/page_template.tsx

x-pack/plugins/observability_solution/infra/public/pages/metrics/page_template.tsx

@@ -95,12 +95,12 @@ export const MetricsPageTemplate: React.FC<LazyObservabilityPageTemplateProps> =
 
   if (isLoading && !source) return <SourceLoadingPage />;
 
-  if (!remoteClustersExist) {
-    return <NoRemoteCluster />;
+  if (sourceError) {
+    return <SourceErrorPage errorMessage={sourceError} retry={loadSource} />;
   }
 
-  if (sourceError) {
-    <SourceErrorPage errorMessage={sourceError} retry={loadSource} />;
+  if (!isLoading && !remoteClustersExist) {
+    return <NoRemoteCluster />;
   }
 
   if (dataViewLoadError) {