Add common OpenTelemetry configurations

[obs-gh-peternguyen]

Enhancement Request

Requesting feature to add common OpenTelemetry configurations such as:
https://opentelemetry.io/docs/specs/otel/configuration/sdk-environment-variables/

OTEL_EXPORTER_OTLP_TRACES_ENDPOINT
OTEL_EXPORTER_OTLP_TRACES_HEADERS
OTEL_EXPORTER_OTLP_TRACES_PROTOCOL

OTEL_EXPORTER_OTLP_METRICS_ENDPOINT
OTEL_EXPORTER_OTLP_METRICS_HEADERS
OTEL_EXPORTER_OTLP_METRICS_PROTOCOL

OTEL_EXPORTER_OTLP_LOGS_ENDPOINT
OTEL_EXPORTER_OTLP_LOGS_HEADERS
OTEL_EXPORTER_OTLP_LOGS_PROTOCOL

OTEL_RESOURCE_ATTRIBUTES

Flags could then be used as follows:

docker run -d --name ktranslate `
  -v /opt/ktranslate/snmp.yaml:/etc/ktranslate/snmp.yaml `
  kentik/ktranslate:next `
--format=otel `
--otel.traces.protocol=http `
--otel.traces.endpoint=https://${ENDPOINT}/v1/traces `
--otel.traces.headers=Authorization=Bearer ${TOKEN} `
--otel.metrics.protocol=http `
--otel.metrics.endpoint=https://${ENDPOINT}/v1/metrics `
--otel.metrics.headers=Authorization=Bearer ${TOKEN} `
--otel.logs.protocol=http `
--otel.logs.endpoint=https://${ENDPOINT}/v1/logs `
--otel.logs.headers=Authorization=Bearer ${TOKEN} `
--otel.resource.attributes=service.name=ktranslate,service.instance.id=docker,service.namespace=default
--snmp=/etc/ktranslate/snmp.yaml `
--sinks=otel `
--metrics=jchf `
--tee_logs=true `
--service_name=snmp `
--max_flows_per_message=100 `
--snmp_discovery_on_start=true `
--snmp_discovery_min=720"

Currently, only these otel flags (for example) appear to work, which limits the data to a single endpoint.

--otel.protocol="http" `
--otel.endpoint="http://host.docker.internal:4318" 

Use Cases

1. Many external destinations require authentication, so a flag like --otel.headers would be great to have (similar to how --http_header is already working to be able to add multiple headers if needed).
2. Some systems do not have enough resources to spin up another container to host a local collector, so sending directly to the destination from ktranslate would be preferred
3. There are instances when logs must be sent to a separate destination for analysis or for security reasons. Having an option to split out where logs, metrics, and traces are sent would help route the data if needed.