Support for newer Node versions and drop Node 10 support

[PieterGit]

Is your feature request related to a problem? Please describe.
Nightscout currently supports "node": "^10.22.0 || ^12.18.4",. Latest Node 10.x is from 06-Apr-2021 and is not currently supported by the NodeJS project anymore. NodeJS 12 is scheduled end-of-life 2022-04-30 so Nightscout users should have upgraded by then (source: https://nodejs.org/en/about/releases/ ). Heroku uses latest Node 12 by default

Currently Nightscout is tested with node-version: [12.x, 14.x]

Describe the solution you'd like

• Nightscout should actively support Node v16 and should use Node v14 or Node v16 by default for Heroku
• Drop Node v10 support since it's not secure anymore

Describe alternatives you've considered
None. Nightscout policy is/was to support Active and Maitenance LTS versions.

Additional context
I don't know the current version of Node with Azure and if still people are using Nightscout with Azure. References to Azure are almost a year old in issues. See #4798 for details.

[PieterGit]

@bewest and @sulkaharo. I think I have some time this Christmas holidays to do some small Nightscout hacking again. Can you please sahre your thoughts on this one?

[bewest]

I might need some time to drop node 10. There's been some interest in alternative hosting approaches to Heroku, including Digital Ocean and others. I'd like to see support for t:connect and LibreView. Also, there's a useful reporting feature request for Loop.