Add simple ollama chat example

[matthewhaynesonline]

Fixes #191.

I used the code examples from #173 as a starting point and tried to simplify them to match the existing chat example.

[matthewhaynesonline]

Hi @64bit, I've updated my PR with your feedback, though the Docker setup has some caveats I didn't have elegant solutions for.

1. Build context: since Docker restricts where you can copy files from to the current directory branch (parents / siblings are not allowed), I adjusted the example to pull the async_openai crate from crates.io, not the parent dir.
   1. The only way I could think to use the crate from the parent project dir was to place the docker-compose.yml / Dockerfile in the project root, but that would no longer make the example self contained.
2. First time Ollama model pull: Ollama requires you to pull a model before you can use it and, understandably, the Ollama docker image doesn't come preloaded with any models. As such, a custom entrypoint is use to pull the model on startup. A healthcheck is then used to wait to start the Rust container until after the Ollama container is fully ready.

What do you think?

[64bit]

Thanks for update, I just tried it and looks good!

I think Dockerfile and ollam_chat containers in docker-compose are not required. My initial reason for docker-compose was to bring up Ollama and then cargo run example which would point to "localhost:ollama-port".

Your entrypoint stuff to download model looks good to me.

So user has to do two steps:

# bring ollama up with model
docker compose up -d

# once model is downloaded and ollama is up
cargo run 

[matthewhaynesonline]

@64bit Sounds good! I updated my branch with your feedback to run the Rust code natively and rebased / cleaned up the commit history off latest upstream main.

[64bit]

Looking good, thank your for your contributions!