Add OTLP/Traces output support, using stable OTEL golang SDK.

Folding Falco events into traces allows them to be represented as "hierarchical" views.
Using a TraceID taken from `container.id` (or Kubernetes labels down to `k8s.pod.name` if present), all Falco events will be "rooted" under the container where it occurred, enabling a tree~ish view of these.

It's implemented alongside other outputs (`outputs/otlp.go`), using existing configuration approach (YAML config and/or environment vars), excerpt from `config_example.yaml` changes:

```yaml
otlp:
  traces:
    # endpoint: "" # OTLP endpoint in the form of http://{domain or ip}:4318/v1/traces
    # protocol: "" # OTLP protocol http/json, http/protobuf, grpc (default: "" which uses SDK default: http/json)
    # timeout: "" # OTLP timeout: timeout value in milliseconds (default: "" which uses SDK default: 10000)
    # headers: "" # OTLP headers: list of headers to apply to all outgoing traces in the form of "some-key=some-value,other-key=other-value" (default: "")
    # synced: false # Set to true if you want traces to be sent synchronously (default: false)
    # duration: 1000 # Artificial span duration in milliseconds (default: 1000)
    # extraenvvars: # Extra env vars (override the other settings)
      # OTEL_EXPORTER_OTLP_TRACES_TIMEOUT: 10000
      # OTEL_EXPORTER_OTLP_TIMEOUT: 10000
```

As the implementation uses upstream golang OTEL SDK, all OTEL environment
variables [can also be used](https://opentelemetry.io/docs/concepts/sdk-configuration/otlp-exporter-configuration/), namely
* OTEL_EXPORTER_OTLP_HEADERS, OTEL_EXPORTER_OTLP_TRACES_HEADERS
* OTEL_EXPORTER_OTLP_TIMEOUT, OTEL_EXPORTER_OTLP_TRACES_TIMEOUT
* OTEL_EXPORTER_OTLP_PROTOCOL, OTEL_EXPORTER_OTLP_TRACES_PROTOCOL

See [otlp_traces.md](./docs/outputs/otlp_traces.md) for more details,
including a `docker_compose.yaml` to stage a whole stack (falco,
falcosidekick, Grafana Tempo and Grafana visualization).

This PR idea and 1st draft was originally crafted during a hackathon at
@grafana Labs, together with @mostafa and @petewall.

--
Signed-off-by: JuanJo Ciarlante <[email protected]>

fix `key: value` in config_example.yaml

Co-authored-by: Thomas Labarussias <[email protected]>
Signed-off-by: JuanJo Ciarlante <[email protected]>

Co-authored-by: Thomas Labarussias <[email protected]>
Signed-off-by: JuanJo Ciarlante <[email protected]>

Co-authored-by: Thomas Labarussias <[email protected]>
Signed-off-by: JuanJo Ciarlante <[email protected]>

Co-authored-by: Thomas Labarussias <[email protected]>
Signed-off-by: JuanJo Ciarlante <[email protected]>

Signed-off-by: JuanJo Ciarlante <[email protected]>

…ntArgs`

Signed-off-by: JuanJo Ciarlante <[email protected]>

…as documented)

Signed-off-by: JuanJo Ciarlante <[email protected]>

Signed-off-by: JuanJo Ciarlante <[email protected]>

Signed-off-by: JuanJo Ciarlante <[email protected]>

Signed-off-by: JuanJo Ciarlante <[email protected]>

Signed-off-by: JuanJo Ciarlante <[email protected]>

Signed-off-by: JuanJo Ciarlante <[email protected]>