Extend MongoDB / mlab maintenance in Nightscout documentation for Nightscout 0.11+

[PieterGit]

Quite some users run into problems with a full MongoDB. The OpenAps docs have some troubleshooting info https://openaps.readthedocs.io/en/latest/docs/Troubleshooting/Rig-NS-communications-troubleshooting.html and more specifc this part on Mlab Maintenance: https://openaps.readthedocs.io/en/latest/docs/Troubleshooting/Rig-NS-communications-troubleshooting.html#mlab-maintenance

Thanks to @jpcunningh Nightscout 0.11 will have several new features that can help people maintain their MongoDB and keep within the limits and is much more resilient if you have a full MongoDB. It will also write information about the error in the console log. With Nightscout 0.11 users are able to delete treatments, entries and most importantly delete devicestatus'es from the Nightscout UI. See linked issues below for more information on these new features.

The Nightscout documentation should be extended about MongDB. Things that need to be done:

• integrate Nightscout maintenance and troubleshooting docs in the Nightscout docs (so that openaps and other APS projects, can link to it instead of embedding it within their documentation)
• describe the new MongoDB maintenance features with Nightscout 0.11 and how to use them (with screenshots)
• describe possible options for MongDB hosting (SaaS, own hosted, etc.)
• ...

I'm hoping a new user like @Dave9111 can work on a PR like this. I'm sure a lot of people can help him if he's unsure about what to write.

This is a followup on gitter discussion that starts here: https://gitter.im/nightscout/cgm-remote-monitor?at=5c324b145ec8fe5a85100157

[Dave9111]

I've got this on my TODO list tagged to you Pieter... Once we install the DEV version I will try out the new MongoDB maintenance features. I may be asking some questions. Can you point me to the tools you want used for the docs? What format etc. I doubt that I am qualified to evaluate different MongoDB hosting solutions. I have seen "Atlas" mentioned as solution. But honestly, if the DB is self maintaining should there ever be a need to exceed 500 mb is size? If it holds 2-3 months of Devicestatus data, I would think that would be sufficient for > 95% of the people.

[PieterGit]

@Dave9111 the docs need quite some love and attention, so if you do any of the other tasks besides hosting or MongoDB troubleshooting will be very good. If anything is unclear, feel free to ask at https://gitter.im/nightscout/public

For tools. See https://openaps.readthedocs.io/en/latest/docs/Resources/my-first-pr.html for a description on how to use the Github webeditor. We can use all the OpenAps docs and customize them for Nightscout if we want. If you want to have a local client you can use something like Notepad++ or any other text editor. There are quite some possibilities for Git clients as well. I use SourceTree but that's more for advanced merging.