[FEATURE]: Add environment variables for disabling warnings

[eysi09]

Feature Request

Background / Motivation

Garden sometimes logs warnings or informational messages that can be disabled via a one-time operation by running the garden util hide-warning command in case they get in people's way.

This doesn't really work in CI though since this information is stored locally. So to avoid these warnings in CI, you'd need to run the util hide-warning command in every job.

To address this, we can add environment variables for disabling common warnings that can be set in CI.

What should the user be able to do?

Also disable warnings via env vars.

Why do they want to do this? What problem does it solve?

Noisy / confusing output in CI. As a side note, our warnings of course shouldn't be noisy and confusing in the first place and we may want to revisit or remove some of them.

Suggested Implementation(s)

As noted about, add env vars for disabling these. Some warnings will eventually be removed because they no longer apply and we should take care of removing the env vars as well (without it being a breaking change).

[alexkuretz]

Please do this. We have >20 projects in garden and it's a pain running the hide command in each of them.