[AUR-338, AUR-406, AUR-407] Export pipeline to config for PromptUI. Construct PromptUI dynamically based on config. (#16)

From pipeline > config > UI. Provide example project for promptui

- Pipeline to config: `kotaemon.contribs.promptui.config.export_pipeline_to_config`. The config follows schema specified in this document: https://cinnamon-ai.atlassian.net/wiki/spaces/ATM/pages/2748711193/Technical+Detail. Note: this implementation exclude the logs, which will be handled in AUR-408.
- Config to UI: `kotaemon.contribs.promptui.build_from_yaml`
- Example project is located at `examples/promptui/`

knowledgehub/documents/base.py

@@ -1,4 +1,5 @@
 from haystack.schema import Document as HaystackDocument
+from llama_index.bridge.pydantic import Field
 from llama_index.schema import Document as BaseDocument
 
 SAMPLE_TEXT = "A sample Document from kotaemon"
@@ -20,3 +21,17 @@ class Document(BaseDocument):
         metadata = self.metadata or {}
         text = self.text
         return HaystackDocument(content=text, meta=metadata)
+
+
+class RetrievedDocument(Document):
+    """Subclass of Document with retrieval-related information
+
+    Attributes:
+        score (float): score of the document (from 0.0 to 1.0)
+        retrieval_metadata (dict): metadata from the retrieval process, can be used
+            by different components in a retrieved pipeline to communicate with each
+            other
+    """
+
+    score: float = Field(default=0.0)
+    retrieval_metadata: dict = Field(default={})