fix(llma): use distinct_id from outer context if not provided

[ethanporcaro]

Related to #443

Right now, the LLM analytics wrappers accept a posthog_distinct_id parameter, but override any existing distinct_id, even if the parameter is None.

The utility functions pass

ph_client.capture(
                    distinct_id=posthog_distinct_id or posthog_trace_id,
...

However, if posthog_distinct_id is None (default) it will default to the posthog_trace_id, even if an ID exists on the outer context.

This PR modifies the logic to do the following:

• If a custom distinct_id is passed by parameter, it is used in identify_context
• If no context exists (meaning the above never happened, and no existing context is available), identify with the trace_id.
• Call ph_client.capture without the distinct_id parameter, so that it uses whatever was set from the above steps.

Let me know if any changes are needed or if I should implement this differently.

[greptile-apps]

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[ethanporcaro]

Some of these failed tests are passing on my machine. Do the tests set an outer distinct_id?

[ethanporcaro]

Nevermind, I realize I was running them incorrectly. I think I found the issue and will push a commit soon

[ethanporcaro]

Should be good to go