[hub] [gql] propagate prompt_id to the span created via the playground

[mikeldking]

Right now if you run the playground, the span created has no linking to the prompt that was used. One approach would be to start adding some px or phoenix specific kv pairs to the metadata (alternative would be semcov) so that at least you could filter by a prompt_id (version_id?) to narrow down the spans related to a specific playground use.

[mikeldking]

adding @cephalization to work through passing the prompt id and any other metadata info we want to pass down to the invocation

[mikeldking]

@anticorrelator this is high priority and we should get it in before release.