Metrics + OpenTelemetry Tracing

[pablohoch]

Adds various Prometheus metrics:

• HTTP endpoint: /metrics (only when the metrics module is loaded)
• Metrics include:
  • Number of routing requests (nigiri + intermodal)
  • Routing time histograms
  • Some routing request statistics (e.g. number of via stations)
  • GTFS-RT metrics per feed (updates, errors, number of entities, timestamp of latest update etc.)

Adds OpenTelemetry Tracing:

• Set the otlp_http=1 config option to enable the OTLP HTTP exporter
  • Exporter configuration is currently done via environment variables (see the documentation), e.g. by setting OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4317 (which is the default).
  • Currently only the OTLP HTTP exporter is supported (i.e. Protocol Buffers (default) or JSON via HTTP, no gRPC).

Needs motis-project/nigiri#131

Closes #222

OpenTelemetry Tracing Examples

Screenshots from Jaeger UI:

Intermodal routing request:

GTFS-RT update:

Import:

Context propagation: