fix: correct OTel instrument kind for db.client.connection.count and db.client.connection.pending_requests

[elena-kolevska]

Two client observability metrics (db.client.connection.count and db.client.connection.pending_requests) changed from a gauge to an UpDownCounter. This Pr brings the docs in alignment with the change.

---

Note

Low Risk
Low risk docs/spec update: only the metric metadata in data/client_obs_metrics.json changes, with no runtime code impact. Risk is limited to consumers relying on the previous Gauge/async semantics for these two metric definitions.

Overview
Updates the client observability metrics spec to reflect that db.client.connection.count and db.client.connection.pending_requests are synchronous UpDownCounters rather than observable Gauges.

This changes their declared type, otel.instrument_kind, and async/observable flags, and removes wording that described them as async metrics.

^{Written by Cursor Bugbot for commit 0cd7ba1. This will update automatically on new commits. Configure here.}

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}