Investigate use of loki

[dylanmcreynolds]

In #24, we describe a task to make use of prometheus to store metrics. Similar to that, we would like to look at the ability to centrally store logs. https://github.com/grafana/loki.

I think that to start with, this might be as simple as making use of the this library within splash-server: https://pypi.org/project/python-logging-loki/

This would have to be a configurable option. Certain deployment frameworks (like NERSC Spin) require logging to stdout, so we need to be able to preserve logging there. We might also want to be able to do both simultaneously.

And like in #24 , we would want the loki process running in splash-deploy.

[estebanrocca]

save logs in a file, and use promtail to send to loki