add a flag to allow pushing traces to custom OTEL endpoint

[mangelino]

Description

Add a --otel-endpoint flag to specify a different local OTEL collector than the one provided by the cli

Acceptance Criteria

• When specifying --otel-endpoint flag, traces are pushed to the endpoint instead of the embedded collector, the collector server is not started
• When the flag is not specified, it works as before

Additional Context

I want to use other OTEL collectors, like sidestep.ai to collect and analyse traces locally