Send data or alerts to Telegram Messenger chat

[t-pi]

First commit sending regular data and/or alerts to Telegram messenger on phone

• config via userdefines.h
• send data every (N) transmissions, i.e. every N*2.5 min to Telegram channel
• send local alerts also to Telegram channel

[ThomasWaldmann]

Hmm, isn't Telegram a closed / commercial service? The client seems free, but the server? Is there only one hosted by that company?

Somehow I feel supporting Matrix (Messenger: element) would be more appropriate as they also have FOSS server.

[t-pi]

While Telegram has not the best of reputation with human communities, it also was one of the very first to push for an easy to use chatbot system and API. Therefore it was the easiest to implement - but also the only relatively common messenger I found at all with an Arduino library... The clients claim to be open source and support reproducible builds (s. e.g. here: https://telegram.org/apps), thus here it is as it is. No need to use the Telegram client for anything else than making :) That said, if you find another library e.g. for Matrix (and can point me to a decent client) I am willing to integrate as well, if within my capabilities.

[t-pi]

Hi @ThomasWaldmann, I started a separate PR to better handle different events while processing GMC data. Hopefully this will help address some of the issues above. Could you please have a look at #444 before I continue here? Thanks!