Client monitoring peer count is broken

**Describe the bug**

Client monitoring peer count is broken as it relied on libp2p metrics which are no longer accessible.
https://github.com/ChainSafe/lodestar/blob/8023e3f7f50642ee4955561341f53417e396aded/packages/beacon-node/src/monitoring/clientStats.ts#L128

The metric was broken when we move libp2p to worker thread
- https://github.com/ChainSafe/lodestar/pull/5229

as the registry passed to monitoring service no longer has access to those metrics
https://github.com/ChainSafe/lodestar/blob/8023e3f7f50642ee4955561341f53417e396aded/packages/beacon-node/src/node/nodejs.ts#L194

**Expected behavior**

Should correctly report peer count on beaconchai.in monitoring app.

**Steps to Reproduce**

Enable client monitoring via `--monitoring.endpoint` pointed to beaconcha.in and look into mobile app (network tab).

**Screenshots**

Upgrading v1.8.0 to v1.9.0-rc.0


Start in packages/beacon-node/src/monitoring/clientStats.ts around the peer-count metric, then inspect packages/beacon-node/src/node/nodejs.ts where the monitoring registry is passed. Reproduce with --monitoring.endpoint pointed at beaconcha.in and check the network tab. Done means the beaconcha.in monitoring app correctly reports the client peer count.

Written by the indexing model from the issue text.