Datasette deployment

[ar-jan]

Use Debian 11 for reasonably up to date version of SQLite. Serving Datasette should work with customization of the deployment module.

[ar-jan]

Basic deployment is functional. Remaining TODOs:

• [ ] Handle logging (there seems to only be stdout logging, or it isn't documented?)
• [x] Add a mechanism for start_application() and stop_application() to deployment to manage serving Datasette (possible to use ExternalProcess class like gunicorn?)
• [x] Clean-up deployment settings (use systemd, or Configuration directory mode?)
• [x] Use DATASETTE_SECRET
• [ ] Tune settings for performance, security configuration, download option, custom queries, etc.

[ar-jan]

Deployment done via a systemd service, since Datasette doesn't have a daemonize mode and process id handling like Gunicorn. Documented in the deployment module.

Note: using Datasette's uvicorn server together with Gunicorn may also be possible: https://www.uvicorn.org/#running-with-gunicorn.

Logging and production settings spun out to #15 and #16.