[9.0] [APM] Improve performance in `dependencies` endpoints…

… to prevent high CPU usage (#209999) (#210320)

# Backport

This will backport the following commits from `main` to `9.0`:
- [[APM] Improve performance in `dependencies` endpoints to
prevent high CPU usage
(#209999)](#209999)

<!--- Backport version: 9.4.3 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

<!--BACKPORT [{"author":{"name":"Milosz
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Improve performance in `dependencies` endpoints to prevent high CPU
usage (#209999)\n\n## Summary\r\n\r\nAfter investigating a high CPU
spike in the `dependencies` endpoints for\r\nlarge quantities of data,
we identified the issue as a slow deep merge\r\nof objects. The merge
operation was growing exponentially in size based\r\non the number of
objects found with the same `id`.\r\n\r\nWe improved performance by
excluding the stats object from unnecessary\r\nmerges and instead
joining it using the spread operator. The results\r\nshow a significant
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Improve performance in `dependencies` endpoints to prevent high CPU
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Improve performance in `dependencies` endpoints to prevent high CPU
usage (#209999)\n\n## Summary\r\n\r\nAfter investigating a high CPU
spike in the `dependencies` endpoints for\r\nlarge quantities of data,
we identified the issue as a slow deep merge\r\nof objects. The merge
operation was growing exponentially in size based\r\non the number of
objects found with the same `id`.\r\n\r\nWe improved performance by
excluding the stats object from unnecessary\r\nmerges and instead
joining it using the spread operator. The results\r\nshow a significant
reduction in CPU usage, preventing the event loop\r\nfrom being blocked
and ensuring better resource
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Improve performance in `dependencies` endpoints to prevent high CPU
usage (#209999)\n\n## Summary\r\n\r\nAfter investigating a high CPU
spike in the `dependencies` endpoints for\r\nlarge quantities of data,
we identified the issue as a slow deep merge\r\nof objects. The merge
operation was growing exponentially in size based\r\non the number of
objects found with the same `id`.\r\n\r\nWe improved performance by
excluding the stats object from unnecessary\r\nmerges and instead
joining it using the spread operator. The results\r\nshow a significant
reduction in CPU usage, preventing the event loop\r\nfrom being blocked
and ensuring better resource
availability.\r\n\r\n|Before|After|\r\n|-|-|\r\n|<img width=\"1728\"
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BACKPORT-->

Co-authored-by: Milosz Marcinkowski <38698566+miloszmarcinkowski@users.noreply.github.com>

x-pack/solutions/observability/plugins/apm/server/lib/connections/get_connection_stats/index.ts

@@ -72,7 +72,7 @@ export function getConnectionStats({
       const { stats: statsA, ...itemA } = a;
       const { stats: statsB, ...itemB } = b;
 
-      return merge({}, itemA, itemB, { stats: statsA.concat(statsB) });
+      return { ...merge({}, itemA, itemB), stats: statsA.concat(statsB) };
     });
 
     const statsItems = statsJoinedById.map((item) => {