community[minor]: Prem AI langchain integration (#19113)

### Prem SDK integration in LangChain

This PR adds the integration with [PremAI's](https://www.premai.io/)
prem-sdk with langchain. User can now access to deployed models
(llms/embeddings) and use it with langchain's ecosystem. This PR adds
the following:

### This PR adds the following:

- [x]  Add chat support
- [X]  Adding embedding support
- [X]  writing integration tests
    - [X]  writing tests for chat 
    - [X]  writing tests for embedding
- [X]  writing unit tests
    - [X]  writing tests for chat 
    - [X]  writing tests for embedding
- [X]  Adding documentation
    - [X]  writing documentation for chat
    - [X]  writing documentation for embedding
- [X] run `make test`
- [X] run `make lint`, `make lint_diff` 
- [X]  Final checks (spell check, lint, format and overall testing)

---------

Co-authored-by: Anindyadeep Sannigrahi <anindyadeepsannigrahi@Anindyadeeps-MacBook-Pro.local>
Co-authored-by: Bagatur <baskaryan@gmail.com>
Co-authored-by: Erick Friis <erick@langchain.dev>
Co-authored-by: Bagatur <22008038+baskaryan@users.noreply.github.com>

libs/community/langchain_community/embeddings/__init__.py

@@ -80,6 +80,7 @@ _module_lookup = {
     "VolcanoEmbeddings": "langchain_community.embeddings.volcengine",
     "VoyageEmbeddings": "langchain_community.embeddings.voyageai",
     "XinferenceEmbeddings": "langchain_community.embeddings.xinference",
+    "PremAIEmbeddings": "langchain_community.embeddings.premai",
     "YandexGPTEmbeddings": "langchain_community.embeddings.yandex",
 }