pkg/util/log: Add support for OTLP sink

[arjunmahishi]

Describe the solution you'd like
Implement an OTLP sink for CockroachDB logging that sends logs in OpenTelemetry format via gRPC (and optionally HTTP/JSON). It should expose configuration parameters (e.g., endpoint, port, auth headers) and integrate with the existing logging framework similar to HTTP and Fluent sinks.

OTLP leverages protocol buffers for efficient binary serialization, reducing payload sizes and enhancing performance compared to text-based formats. Its support for gRPC enables low-latency, high-throughput communication, while HTTP/JSON provides compatibility when needed.

Why we should do this

• The SRE team is currently migrating Fluent Bit to OTel using the existing Fluent sink. Adding native OTLP support will optimise the logging pipeline further and help standardise the OpenTelemetry ecosystem.
• Serverless log export (to customers) currently uses Fluent Bit as a log forwarder [ CRDB -> fluentbit -> otel-agent -> customer ]. Adding OTLP support would significantly simplify this pipeline.
• Self hosted customers can also take advantage of this while setting up their logging pipeline.

References

• OTLP Spec
• OTLP receiver module in Otel collector.
• Datadog agent supports OTLP integration.

Jira issue: CRDB-48633