Add an ollama plugin

[cmungall]

Ollama makes it easy to run models such as llama2 locally on macOS easily:

https://ollama.ai/

The user runs a server on localhost, so the architecture of the plugin could likely follow the existing replicate plugin.

from the ollama docs:

 curl -X POST http://localhost:11434/api/generate -d '{
    "model": "llama2",
    "prompt":"Why is the sky blue?"
   }'

the output is quite straightforward and amenable to streaming:

{"model":"llama2","created_at":"2023-08-24T20:24:05.78795Z","response":" The","done":false}
{"model":"llama2","created_at":"2023-08-24T20:24:05.805889Z","response":" sky","done":false}
{"model":"llama2","created_at":"2023-08-24T20:24:05.824734Z","response":" appears","done":false}
{"model":"llama2","created_at":"2023-08-24T20:24:05.842502Z","response":" blue","done":false}
{"model":"llama2","created_at":"2023-08-24T20:24:05.860295Z","response":" because","done":false}
...