Add OpenID Connect integration

[alexashley]

Remaining work

• [ ] ~add login/logout buttons~
• [ ] ~display authenticated username and maybe role~
• [x] expose auth-related config
• [x] don't require login
• [x] tests for express integration
• [x] change server-side code to use ESM
• [x] update Dockerfile
• [x] set the next dev flag dynamically

Those first two will be a follow up, navigating to /login or /logout should work in the meantime. Auth is disabled by default.

Closes #140

[alexashley]

Made some issues for follow up PRs: #155, #156