v2.1.1

This is a tiny release with a few bug fixes, but it's big for me personally. After almost three months of work,
today I am finally launching the paid plans on ntfy.sh 🥳 🎉.

You are now able to purchase one of three plans that'll give you higher rate limits (messages, emails, attachment sizes, ...),
as well as the ability to reserve topic names for your personal use, while at the same time supporting me and the
ntfy open source project ❤️. You can check out the pricing, and purchase plans through the web app (use
promo code MYTOPIC for a 50% discount, limited time only).

And as I've said many times: Do not worry. ntfy will always stay open source, and that includes all features. There
are no closed-source features. So if you'd like to run your own server, you can!

Bug fixes + maintenance:

• Fix panic when using Firebase without users (#641, thanks to u/heavybell for reporting)
• Remove health check from Dockerfile and document it (#635, thanks to @Andersbiha)
• Upgrade dialog: Disable submit button for free tier (no ticket)
• Allow multiple log-level-overrides on the same field (no ticket)
• Actually remove ntfy publish --env-topic flag (as per deprecations, no ticket)
• Added billing-contact config option (no ticket)