[GEN-2175]: optimize metrics fetching based on available sources and …

…destinations (#2160)

This pull request includes changes to the `useMetrics` hook in the
`frontend/webapp/hooks/overview/useMetrics.ts` file to improve its
functionality by ensuring that metrics are only fetched when there are
sources or destinations available.

Improvements to `useMetrics` hook:

*
[`frontend/webapp/hooks/overview/useMetrics.ts`](diffhunk://#diff-a1494f6951b923bb9bdd816930133866b8e6ab2f8e2d61d2c9730e4ee02469beL2-R12):
Modified the `useMetrics` hook to use the `useSourceCRUD` and
`useDestinationCRUD` hooks for fetching sources and destinations, and
updated the `skip` condition in the `useQuery` call to prevent fetching
metrics when there are no sources or destinations.

frontend/webapp/hooks/overview/useMetrics.ts

@@ -1,11 +1,15 @@
 import { useQuery } from '@apollo/client';
-import { GET_METRICS } from '@/graphql/mutations/metrics';
+import { useSourceCRUD } from '../sources';
+import { useDestinationCRUD } from '../destinations';
 import type { OverviewMetricsResponse } from '@/types';
+import { GET_METRICS } from '@/graphql/mutations/metrics';
 
 export const useMetrics = () => {
-  // TODO: don't fetch until we have sources and/or destinations
+  const { sources } = useSourceCRUD();
+  const { destinations } = useDestinationCRUD();
+
   const { data } = useQuery<OverviewMetricsResponse>(GET_METRICS, {
-    skip: false,
+    skip: !sources.length && !destinations.length,
     pollInterval: 3000,
   });