Add network quality metrics to gaming SDK perf monitoring

Sentry's performance monitoring is span/transaction-based and does not capture network quality metrics such as round-trip latency (ping) or packet loss. Gaming customers want these signals correlated with crash and performance data.

- Current perf monitoring covers HTTP timing, DB spans, and custom spans
- No built-in instrumentation for raw network quality (RTT, jitter, packet loss)
- High-frequency polling could cause significant event volume; sampling strategy is required

Add an opt-in network quality monitoring API to the gaming SDKs (Xbox, PlayStation, Unity, Unreal) that captures ping/RTT and packet loss as custom metrics or sampled spans, with configurable sample rates to control event volume.

Reported by a gaming console customer (Triiodide Technologies).

Action taken on behalf of Richard Propst.

Start by reviewing the existing span/transaction performance monitoring in the Xbox, PlayStation, Unity, and Unreal gaming SDKs. Define how opt-in RTT and packet-loss measurements should be represented, sampled, and correlated with crash and performance data. Done means the supported SDKs expose configurable network-quality monitoring without uncontrolled event volume.

Written by the indexing model from the issue text.