Add OpenTelemetry Native Metrics Support

[ofekshenawa]

This PR implements Phase 1: Observability (Metrics) for go-redis, adding comprehensive OpenTelemetry metrics support following the OpenTelemetry Database Client Semantic Conventions.

The implementation uses a Bridge Pattern to keep the core library dependency-free while providing optional, metrics instrumentation through the new extra/redisotel-native package.

What's Included:
Metric groups covering aspects of Redis operations:

• Command metrics: Operation duration with retry tracking
• Connection basic: Connection count and creation time
• Resiliency: Errors, handoffs, timeout relaxation
• Connection advanced: Wait time and use time
• Stream metrics: Processing duration and maintenance notifications