Support OpenTelemetry

[lukaslihotzki-f]

Remaining todos:

• documentation
• testing

Metrics will be done in a separate PR.

This PR does nothing without explicit configuration.

Add this to homeserver.yaml:

opentracing:
  enabled: true
  backend: otlp

Add this to your log config YAML:

handlers:
  otlp:
    class: synapse.logging.handlers.OtlpHandler
root:
  handlers: […, otlp]

Note that the logging OtlpHandler does not use a formatter, because it is designed for structured logging.

Then, set the otlp endpoint using environment variables (e.g., OTEL_EXPORTER_OTLP_ENDPOINT).

[CLAassistant]

All committers have signed the CLA.

[nico-famedly]

Looks good to me, but I didn't test it yet. Long term we might want to integrate otlp better by removing the opentracing support and reorganizing some things to allow dynamic tracing of endpoints, but for now this looks good. Thanks a lot!