chore: use ro connstring for observability (#44806)

## I have read the
[CONTRIBUTING.md](https://github.com/supabase/supabase/blob/master/CONTRIBUTING.md)
file.

YES

## What kind of change does this PR introduce?

function change

## What is the current behavior?

defaults to the read-write connection string when doing observability
report queries

## What is the new behavior?

uses the read-only connection string instead

## Additional context

these should only ever be read-only operations, reporting should not
have side effects and this adds a guardrail to ensure that remains the
case


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

**Bug Fixes**
- Corrected database replica query handling by using read-only
connection strings for replica database access.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

apps/studio/components/interfaces/QueryPerformance/useQueryPerformanceQuery.ts

@@ -138,7 +138,7 @@ export const useQueryPerformanceInfiniteQuery = (
   const { data: databases } = useReadReplicasQuery({ projectRef: project?.ref })
   const connectionString = (databases || []).find(
     (db) => db.identifier === state.selectedDatabaseId
-  )?.connectionString
+  )?.connection_string_read_only // default to read_only connection string
 
   // Clamp pageSize the same way generateQueryPerformanceSql does so getNextPageParam
   // and the queryKey are always consistent with the SQL actually executed.