Add setup to run Known with Docker & Tailscale for local development

[jimwins]

Here's what I fixed or added:

Added scripts and config to run Known inside Docker, accessible for Tailscale, for local development.

Here's why I did it:

Easy-ish way to set up an isolated Known system without having to configure things outside of Docker.

Checklist: ([x] to check/tick the boxes)

• This pull request addresses a single issue
• If this code includes interface changes, I've included screenshots in this Pull Request thread
• I've adhered to Known's style guide (these codesniffer rules might help!)
• My git branch is named in a descriptive way - i.e., yourname-summary-of-issue
• I've tested my code in-browser
• My code contains descriptive comments
• I've added tests where applicable, and...
• I can run the unit tests successfully.

[benwerd]

LG. 🙏