RAG upgrade and Azure AI Search

[pelikhan]

I did a round of iteration on basic rag support. You now have more control to create index, add documents and query. By default, genaiscript will use vectra (file based local db) but it also support Azure AI Search. Chunking/vectorization is handled by genaiscript so you don't have to worry about that part when using azure ai search (you can get a free deployment < 50mb of that service)