New instrumentation module (#11831)

docs/api_reference/index.rst

docs/api_reference/instrumentation.rst

docs/examples/instrumentation/basic_usage.ipynb

docs/examples/instrumentation/observe_api_calls.ipynb

docs/index.rst

docs/module_guides/observability/instrumentation.md

docs/module_guides/observability/observability.md

llama-index-core/llama_index/core/agent/runner/base.py

llama-index-core/llama_index/core/base/base_query_engine.py

llama-index-core/llama_index/core/base/base_retriever.py

llama-index-core/llama_index/core/base/embeddings/base.py

llama-index-core/llama_index/core/base/response/schema.py

llama-index-core/llama_index/core/chat_engine/types.py

...-index-core/llama_index/core/indices/vector_store/base.py

...a_index/core/indices/vector_store/retrievers/retriever.py

llama-index-core/llama_index/core/instrumentation/BUILD

...a-index-core/llama_index/core/instrumentation/__init__.py

...index-core/llama_index/core/instrumentation/dispatcher.py

...ore/llama_index/core/instrumentation/event_handlers/BUILD

...ama_index/core/instrumentation/event_handlers/__init__.py