Allow to redirect `gen_ai.input` and `gen_ai.output` to an external destination

[daavoo]

Discussed with @davidmanzanoai .

It would be nice for us to introduce a flexible way for users to specify a target location to store potentially sensitive fields (inputs/outpus) and use a reference in the "plain" trace instead of directly storing the fields.

It appears that this idea is already considered and WIP as part of the OTEL semantic conventions (open-telemetry/semantic-conventions#2179).

[github-actions]

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[javiermtorres]

We could use a custom https://opentelemetry-python.readthedocs.io/en/latest/sdk/trace.html#opentelemetry.sdk.trace.SpanProcessor to handle this information. Wdyt?