Enhance knowledge management in CrewAI

- Added `KnowledgeConfig` class to configure knowledge retrieval parameters such as `limit` and `score_threshold`.
- Updated `Agent` and `Crew` classes to utilize the new knowledge configuration for querying knowledge sources.
- Enhanced documentation to clarify the addition of knowledge sources at both agent and crew levels.
- Introduced new tips in documentation to guide users on knowledge source management and configuration.

src/crewai/knowledge/knowledge_config.py

@@ -0,0 +1,6 @@
+from pydantic import BaseModel
+
+
+class KnowledgeConfig(BaseModel):
+    limit: int = 3
+    score_threshold: float = 0.35