docs: Update docs for HuggingFacePipeline (langchain-ai#19306)

Updated `HuggingFacePipeline` docs to be in sync with list of supported
tasks, including translation.

- [x] **PR title**: "community: Update docs for `HuggingFacePipeline`"
- Where "package" is whichever of langchain, community, core,
experimental, etc. is being modified. Use "docs: ..." for purely docs
changes, "templates: ..." for template changes, "infra: ..." for CI
changes.
  - Example: "community: add foobar LLM"


- [x] **PR message**:
- **Description:** Update docs for `HuggingFacePipeline`, was earlier
missing `translation` as a valid task
    - **Issue:** N/A
    - **Dependencies:** N/A
    - **Twitter handle:** None


- [x] **Add tests and docs**:


- [x] **Lint and test**: Run `make format`, `make lint` and `make test`
from the root of the package(s) you've modified. See contribution
guidelines for more: https://python.langchain.com/docs/contributing/

libs/community/langchain_community/llms/huggingface_pipeline.py

@@ -27,7 +27,8 @@ class HuggingFacePipeline(BaseLLM):
 
     To use, you should have the ``transformers`` python package installed.
 
-    Only supports `text-generation`, `text2text-generation` and `summarization` for now.
+    Only supports `text-generation`, `text2text-generation`, `summarization` and
+    `translation`  for now.
 
     Example using from_model_id:
         .. code-block:: python