allow to use colab secrets via config provider

[rudolfix]

Background
Colab added a feature to specify secrets that you can then access in the code:

Tasks
Implement extra config provider that works like the airflow one.

1. adds itself when colab runtime is present (we have detector utils)
2. is based off the regular toml provider
3. emulates secrets.toml and config.toml, you just load them from the properly named colab secrets
4. contrary to existing toml reader which does not reload, this one must check for changes. so introduce a cache (ie with a few seconds default expiration) that will reload the whole document on get. add cache to the base toml (disabled by default)
5. make sure we do not have obnoxious behavior ie. asking for permissions every second
6. I suggest prototyping in colab. you can add providers dynamically to container