Make validation warnings more clear

[nirs]

It is easy to grep for the warning text and understand why it happens but the warning should make it clear that this is a validation warning, and the issue is unknown property. Maybe something like:

validate vmType vz: ignoring unknown property networks[1]: "Metric"

Notes:

• Unify warning test in wsl2 and vz (vz uses "ignoring" and wsl2 uses "Ignoring")
• This is going to be a big rabbit hole; look at Call limadriver.Validate as part of limayaml.Validate #2512 for more thoughts on how it should be refactored
• Maybe wait until @jandubois replaces current FileDeafults with upcoming code from template assembly because that might change things around anyways
• Warning message may not be clear enough - it can help to link to the docs for the invalid thing.

Originally posted by @nirs in #3010 (comment)