Add kubelet-env config to make kubelet loglevel configurable

[54nd20]

Added ability to configure kubelet loglevel and set the default to loglevel 2
Closes #3

Checklist

• Keep pull requests small so they can be easily reviewed.
• Update the documentation.
• Update the ./CHANGELOG.md.
• Link this PR to related issues.

[corvus-ch]

The knowledge base article contains two solutions (<4.6 and ≥4.6). At the moment, we have both versions running. In its current form, the change would brake things.

[DebakelOrakel]

Is this still an issue, as 4.5 is quiet outdated?

[54nd20]

This pull request would only work for cluster versions <4.6, so it is not relevant anymore.