Callback.on_chain_start has wrong "inputs" in RefineDocumentsChain
Labels: name: auto:bug, name: area: models

### System Info

Python 3.10, mac OS

### Who can help?

@agola11 @hwchase17 

### Information

- [X] The official example notebooks/scripts
- [X] My own modified scripts

### Related Components

- [ ] LLMs/Chat Models
- [ ] Embedding Models
- [ ] Prompts / Prompt Templates / Prompt Selectors
- [ ] Output Parsers
- [ ] Document Loaders
- [ ] Vector Stores / Retrievers
- [ ] Memory
- [ ] Agents / Agent Executors
- [ ] Tools / Toolkits
- [X] Chains
- [X] Callbacks/Tracing
- [ ] Async

### Reproduction

With this script

```
from langchain.chains import RefineDocumentsChain, LLMChain
from langchain.llms import OpenAI
from langchain.prompts import PromptTemplate


document_prompt = PromptTemplate.from_template("{page_content}")
document_variable_name = "context"
llm = OpenAI()
# The prompt here should take as an input variable the
# `document_variable_name`
prompt = PromptTemplate.from_template(
    "Summarize this content: {context}"
)
initial_llm_chain = LLMChain(llm=llm, prompt=prompt)
initial_response_name = "prev_response"
# The prompt here should take as an input variable the
# `document_variable_name` as well as `initial_response_name`
prompt_refine = PromptTemplate.from_template(
    "Here's your first summary: {prev_response}. "
    "Now add to it based on the following context: {context}"
)
refine_llm_chain = LLMChain(llm=llm, prompt=prompt_refine)
chain = RefineDocumentsChain(
    initial_llm_chain=initial_llm_chain,
    refine_llm_chain=refine_llm_chain,
    document_prompt=document_prompt,
    document_variable_name=document_variable_name,
    initial_response_name=initial_response_name,
)

from langchain.schema import Document

text = """Nuclear power in space is the use of nuclear power in outer space, typically either small fission systems or radioactive decay for electricity or heat. Another use is for scientific observation, as in a Mössbauer spectrometer. The most common type is a radioisotope thermoelectric generator, which has been used on many space probes and on crewed lunar missions. Small fission reactors for Earth observation satellites, such as the TOPAZ nuclear reactor, have also been flown.[1] A radioisotope heater unit is powered by radioactive decay and can keep components from becoming too cold to function, potentially over a span of decades.[2]

The United States tested the SNAP-10A nuclear reactor in space for 43 days in 1965,[3] with the next test of a nuclear reactor power system intended for space use occurring on 13 September 2012 with the Demonstration Using Flattop Fission (DUFF) test of the Kilopower reactor.[4]

After a ground-based test of the experimental 1965 Romashka reactor, which used uranium and direct thermoelectric conversion to electricity,[5] the USSR sent about 40 nuclear-electric satellites into space, mostly powered by the BES-5 reactor. The more powerful TOPAZ-II reactor produced 10 kilowatts of electricity.[3]

Examples of concepts that use nuclear power for space propulsion systems include the nuclear electric rocket (nuclear powered ion thruster(s)), the radioisotope rocket, and radioisotope electric propulsion (REP).[6] One of the more explored concepts is the nuclear thermal rocket, which was ground tested in the NERVA program. Nuclear pulse propulsion was the subject of Project Orion.[7]
"""

docs = [
    Document(
        page_content=split,
        metadata={"source": "https://en.wikipedia.org/wiki/Nuclear_power_in_space"},
    )
    for split in text.split("\n\n")
]
```

When I attach a callback that prints the [inputs](https://github.com/langchain-ai/langchain/blob/00a6e8962cc778cd8f6268cefc304465598c02cf/libs/core/langchain_core/callbacks/base.py#L197) in `on_chain_start`, even if every sub-chain only uses one Document, the `inputs` is always the full Document list.

### Expected behavior

I expect the `inputs` in `on_chain_start` only includes the inputs that are used by this chain, not always the full list, otherwise it's totally meaningless to duplicate the same inputs many times.