community: Skip Login to HuggubgFaceHub when token is not set (#21561)

Thank you for contributing to LangChain!

- [ ] **HuggingFaceEndpoint**: "Skip Login to HuggingFaceHub"
  - Where:  langchain, community, llm, huggingface_endpoint
 


- [ ] **PR message**: ***Delete this entire checklist*** and replace
with
- **Description:** Skip login to huggingface hub when when
`huggingfacehub_api_token` is not set. This is needed when using custom
`endpoint_url` outside of HuggingFaceHub.
- **Issue:** the issue # it fixes
https://github.com/langchain-ai/langchain/issues/20342 and
https://github.com/langchain-ai/langchain/issues/19685
    - **Dependencies:** None


- [ ] **Add tests and docs**: 
  1. Tested with locally available TGI endpoint
  2.  Example Usage
```python
from langchain_community.llms import HuggingFaceEndpoint

llm = HuggingFaceEndpoint(
    endpoint_url='http://localhost:8080',
    server_kwargs={
        "headers": {"Content-Type": "application/json"}
    }
)
resp = llm.invoke("Tell me a joke")
print(resp)
```
 Also tested against HF Endpoints
 ```python
 from langchain_community.llms import HuggingFaceEndpoint
huggingfacehub_api_token = "hf_xyz"
repo_id = "mistralai/Mistral-7B-Instruct-v0.2"
llm = HuggingFaceEndpoint(
    huggingfacehub_api_token=huggingfacehub_api_token,
    repo_id=repo_id,
)
resp = llm.invoke("Tell me a joke")
print(resp)
 ```
Additional guidelines:
- Make sure optional dependencies are imported within a function.
- Please do not add dependencies to pyproject.toml files (even optional
ones) unless they are required for unit tests.
- Most PRs should not touch more than one package.
- Changes should be backwards compatible.
- If you are adding something to community, do not re-import it in
langchain.

If no one reviews your PR within a few days, please @-mention one of
baskaryan, efriis, eyurtsev, hwchase17.

---------

Co-authored-by: Erick Friis <erick@langchain.dev>

libs/community/langchain_community/llms/huggingface_endpoint.py

@@ -1,5 +1,6 @@
 import json
 import logging
+import os
 from typing import Any, AsyncIterator, Dict, Iterator, List, Mapping, Optional
 
 from langchain_core._api.deprecation import deprecated
@@ -11,7 +12,6 @@ from langchain_core.language_models.llms import LLM
 from langchain_core.outputs import GenerationChunk
 from langchain_core.pydantic_v1 import Extra, Field, root_validator
 from langchain_core.utils import (
-    get_from_dict_or_env,
     get_pydantic_field_names,
     pre_init,
 )
@@ -177,16 +177,17 @@ class HuggingFaceEndpoint(LLM):
                 "Could not import huggingface_hub python package. "
                 "Please install it with `pip install huggingface_hub`."
             )
-        try:
-            huggingfacehub_api_token = get_from_dict_or_env(
-                values, "huggingfacehub_api_token", "HUGGINGFACEHUB_API_TOKEN"
-            )
-            login(token=huggingfacehub_api_token)
-        except Exception as e:
-            raise ValueError(
-                "Could not authenticate with huggingface_hub. "
-                "Please check your API token."
-            ) from e
+        huggingfacehub_api_token = values["huggingfacehub_api_token"] or os.getenv(
+            "HUGGINGFACEHUB_API_TOKEN"
+        )
+        if huggingfacehub_api_token is not None:
+            try:
+                login(token=huggingfacehub_api_token)
+            except Exception as e:
+                raise ValueError(
+                    "Could not authenticate with huggingface_hub. "
+                    "Please check your API token."
+                ) from e
 
         from huggingface_hub import AsyncInferenceClient, InferenceClient