Collector to support adding common columns to logs

[jessejlt]

A common use-case is for all logs on a host to contain metadata, or columns, about their environment. By adding a new command-line parameter, --add-columns, much like our parameter --add-labels, collector will add common metadata to each OTLP log event it receives.

By running the integration test docker compose -f tools/otlp/logs/compose.yaml up, we can see columns being added to our OTLP logging events.

logs-otel-1       | 2023-08-03T14:29:32.212Z    info    LogsExporter    {"kind": "exporter", "data_type": "logs", "name": "logging", "resource logs": 1, "log records": 1}
logs-otel-1       | 2023-08-03T14:29:32.212Z    info    ResourceLog #0
logs-otel-1       | Resource SchemaURL: 
logs-otel-1       | Resource attributes:
+ logs-otel-1       |      -> Environment: Str(dev)
logs-otel-1       | ScopeLogs #0
logs-otel-1       | ScopeLogs SchemaURL: 
logs-otel-1       | InstrumentationScope  
logs-otel-1       | LogRecord #0
logs-otel-1       | ObservedTimestamp: 1970-01-01 00:00:00 +0000 UTC
logs-otel-1       | Timestamp: 2023-08-03 14:29:31.1994291 +0000 UTC
logs-otel-1       | SeverityText: 
logs-otel-1       | SeverityNumber: Unspecified(0)
logs-otel-1       | Body: Map({"message":"dummy"})
logs-otel-1       | Trace ID: 
logs-otel-1       | Span ID: 
logs-otel-1       | Flags: 0
logs-otel-1       |     {"kind": "exporter", "data_type": "logs", "name": "logging"}

When specified by --add-columns

  collector:
    build:
      dockerfile: tools/otlp/logs/Dockerfile
      context: ../../..
    volumes:
      - ~/.kube/config:/root/.kube/config
    ports:
      - 8080:8080
    # While the _endpoints_ URI doesn't match the expected OTLP syntax, keep in
    # mind that _Collector_ is currently configured to connect to _Ingestor_, so we
    # just modify the _endpoints_ in pkg/otlp/proxy to be OTLP compliant.
    command: --kubeconfig /root/.kube/config \
                      --endpoints http://otel:4317/receive \
                      --insecure-skip-verify \
+                      --add-columns Environment=dev
    depends_on:
      - otel
    environment:
      - LOG_LEVEL=DEBUG