Improvements: streaming support

[sinedied]

• Add streaming support in backend (/api/chat/streaming)
• In improvements section add instructions on how to support streaming. See example: https://moaw.dev/workshop/?src=gh%3Aazure-samples%2Fazure-openai-rag-workshop%2Fbase%2Fdocs%2F&step=12#add-follow-up-questions