[MLOB-1524] feat(llmobs): introduce LLM Observability SDK

[sabrenner]

What does this PR do?

Introduces an LLM Observability SDK into the tracer, with its own tracing API extending the core tracer, and span tagging and processing functionality to flush LLM Observability spans to LLM Observability.

The following PRs have been merged into the branch for this PR, and have been reviewed and approved:

#4696 APM: @ida613 LLMObs: @Yun-Kim #4699 APM: @rochdev LLMObs: @Yun-Kim #4718 APM: @rochdev LLMObs @Yun-Kim #4738 APM: @rochdev LLMObs: @lievan

[Rest of description WIP, will populate with relevant docs links. This PR will have at least 2 more commits pushed, one with the span processing logic, and one with the core SDK and Typescript definitions]

Submitting OpenAI spans will be a direct follow-up PR.

Motivation

Introduce core LLM Observability SDK logic into the tracer.