[docs] LogLevel is undocumented.

[BeyondEvil]

Is your feature request related to a problem?/Why is this needed

The log level is undocumented, which is extra frustrating as it deviates from the norm (debug, info, warning, error) and instead uses a integer based level.

• What's the lowest level? 0? 1?
• What does level 2 (the default) correspond to? info? warning?

/feature

Describe the solution you'd like in detail
Document the range and what each level entails.

[ConnorJC3]

/kind feature

Hi, numeric log levels are a common standard, and are for example how all of the official Kubernetes components expose log verbosity controls. They are not meant to directly map to terms like debug/info/warning/error - higher number means more verbose.

That said, it is true we don't have a consistent standard across the codebase on what each log level means, so I'll leave this issue open to fix that.