New otlp_export health telemetry for customer OpenTelemetry exporters

OpenTelemetry (OTLP) is a standard way to send metrics, logs and traces to a monitoring system you run yourself. When you set this up, Claude Code now records an otlp_export event about how those exports went:

• The first successful export of each kind (metrics, logs or traces) records one success event.
• Each distinct failure records one failure event with an error code. Codes include grpc_N, http_401, http_403, http_Nxx, "timeout", "http_retries_exhausted", headers_helper_*, SSL codes or "other".
• Failure events also record the protocol, the HTTP status and whether a proxy was used.

Console and Prometheus exporters are not tracked. Traces are also not tracked when the traces endpoint matches an internal check. The debug line printed on the first export is unchanged.