Add HTTP streaming support for JetStream

[vivianrwu]

Example snippet of streamed responses with respective full response for

curl --request POST --header "Content-type: application/json" -s localhost:8000/generate --data '{
    "prompt": "What are the top 5 programming languages ",
    "max_tokens": 100,
    "stream": true
}'

b'{\n    "id": "generate-b1f2ac51319944658db3f65560881067",\n    "time_created": 1731094258.4464087,\n    "text": "\\n"\n}'
b'{\n    "id": "generate-2670cd56a9ef40d697c25959d1d46d31",\n    "time_created": 1731094258.4621747,\n    "text": "\\n"\n}'
b'{\n    "id": "generate-be55c20ad9914364813738c842e84ce6",\n    "time_created": 1731094258.4723089,\n    "text": "for"\n}'
b'{\n    "id": "generate-dfcc3e724129453c936d4bb24b892310",\n    "time_created": 1731094258.4828267,\n    "text": " data"\n}'
b'{\n    "id": "generate-c5b3879d27c9479091412ac34ea38e9d",\n    "time_created": 1731094258.492773,\n    "text": " science"\n}'
b'{\n    "id": "generate-174ac5c04b2d40aa92f0685e0bb333ea",\n    "time_created": 1731094258.5034208,\n    "text": " in"\n}'
...
['\n\nfor data science in 2023?\n\n1. Python\n2. R\n3. SQL\n4. Java\n5. Scala\n\n**Explanation:**\n\n* **Python** is a popular choice for data science due to its ease of use, extensive libraries, and wide community.\n* **R** is a powerful statistical language widely used for data analysis, visualization, and modeling.\n* **SQL** is a widely-used language for data querying and manipulation.']

[annapendleton]

lgtm once comment is addressed :)