Add env vars to disable update checking (other category?)

[emanuelb]

There are tools who do check for updates on stratup & can be disabled with ENV var, probably should be in another category? or mention differently? as it's not just grab data for analytics like others, etc.. but check for newer version which is useful and sometimes it's better to disable (example: you already know that version used is latest, no reason to check)

1. syncthing https://github.com/syncthing/syncthing/blob/59bdcdabbaae2519955fb5514b1910e30446c99c/man/syncthing.1#L388-L389 export STNOUPGRADE=1 Disable automatic upgrades.

2. fastlane https://github.com/fastlane/docs/blob/000fff1ee2b737346a3abdc9ed1b2be558eab8b3/docs/advanced/fastlane.md#skip-update-check-when-launching-fastlane set: FASTLANE_SKIP_UPDATE_CHECK=1

[beatcracker]

Well, update checks are currently listed as separate telemetry channels, where applicable, e.g.:

• https://github.com/beatcracker/toptout/blob/master/data/terraform.json#L56-L58
• https://github.com/beatcracker/toptout#update-check-2

I could add some kind of additional flag in telemetry channel properties that would indicate that ("is_update_check": "true"). Unfortunately, most of the time, update check is tied to the actual telemetry (e.g. PowerShell).