[AUR-385, AUR-388] Declare BaseComponent and decide LLM call interface (#2)

- Use cases related to LLM call: https://cinnamon-ai.atlassian.net/browse/AUR-388?focusedCommentId=34873
- Sample usages: `test_llms_chat_models.py` and `test_llms_completion_models.py`:

```python
from kotaemon.llms.chats.openai import AzureChatOpenAI

model = AzureChatOpenAI(
    openai_api_base="https://test.openai.azure.com/",
    openai_api_key="some-key",
    openai_api_version="2023-03-15-preview",
    deployment_name="gpt35turbo",
    temperature=0,
    request_timeout=60,
)
output = model("hello world")
```

For the LLM-call component, I decide to wrap around Langchain's LLM models and Langchain's Chat models. And set the interface as follow:

- Completion LLM component:
```python
class CompletionLLM:

    def run_raw(self, text: str) -> LLMInterface:
        # Run text completion: str in -> LLMInterface out

    def run_batch_raw(self, text: list[str]) -> list[LLMInterface]:
        # Run text completion in batch: list[str] in -> list[LLMInterface] out

# run_document and run_batch_document just reuse run_raw and run_batch_raw, due to unclear use case
```

- Chat LLM component:
```python
class ChatLLM:
    def run_raw(self, text: str) -> LLMInterface:
        # Run chat completion (no chat history): str in -> LLMInterface out

    def run_batch_raw(self, text: list[str]) -> list[LLMInterface]:
        # Run chat completion in batch mode (no chat history): list[str] in -> list[LLMInterface] out

    def run_document(self, text: list[BaseMessage]) -> LLMInterface:
        # Run chat completion (with chat history): list[langchain's BaseMessage] in -> LLMInterface out

    def run_batch_document(self, text: list[list[BaseMessage]]) -> list[LLMInterface]:
        # Run chat completion in batch mode (with chat history): list[list[langchain's BaseMessage]] in -> list[LLMInterface] out
```

- The LLMInterface is as follow:

```python
@dataclass
class LLMInterface:
    text: list[str]
    completion_tokens: int = -1
    total_tokens: int = -1
    prompt_tokens: int = -1
    logits: list[list[float]] = field(default_factory=list)
```

README.md

@@ -1,3 +1,31 @@
-Modules:
+# kotaemon
+
+Quick and easy AI components to build Kotaemon - applicable in client
+project.
+
+## Install
+
+```shell
+pip install kotaemon@git+ssh://git@github.com/Cinnamon/kotaemon.git
+```
+
+## Contribute
+
+### Setup
+
+```shell
+# Create conda environment (suggest 3.10)
+conda create -n kotaemon python=3.10
+conda activate kotaemon
+
+# Install all
+pip install -e ".[dev]"
+
+# Test
+pytest tests
+```
+
+### Code base structure
+
 - documents: define document
 - loaders