[RAG] Add chat memory to RAG (WIP)

datafari-tomcat/conf-datafari/rag.properties

...app/src/main/java/com/francelabs/datafari/api/RagAPI.java

...in/java/com/francelabs/datafari/rag/OpenAiLlmService.java

...in/java/com/francelabs/datafari/rag/RagConfiguration.java

.../java/com/francelabs/datafari/rest/v2_0/ai/AiPowered.java

...n/java/com/francelabs/datafari/utils/rag/PromptUtils.java