Add client methods to read / list runs and sessions.
Update walkthrough to:
- Let the user create a dataset from the runs without going to the UI
- Use the new CLI command to start the server
Improve the error message when `docker` isn't found
* add implementations of `BaseCallbackHandler` to support tracing:
`SharedTracer` which is thread-safe and `Tracer` which is not and is
meant to be used locally.
* Tracers persist runs to locally running `langchain-server`
Co-authored-by: Harrison Chase <hw.chase.17@gmail.com>
Keshav Kumar