Wire JvmOtlpRuntimeMetrics into agent startup

Call JvmOtlpRuntimeMetrics.start() from OpenTelemetryMetricsInstrumentation
when both DD_METRICS_OTEL_ENABLED and DD_RUNTIME_METRICS_ENABLED are true.
Matches .NET/Go/NodeJS config gating pattern. Also updates metrics to match
OTel spec exactly (Option B): removes jvm.gc.duration/count, fixes types,
adds missing metrics.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: link04