Support warning & information severity for validation results in the pipeline

[einari]

The validation pipeline is limited in many ways, we need to be able to support the new severity model properly.

The goal is to be able to have validation warnings and information. Information is just information we want to communicate. While warnings could be potential errors and we would like to have the option of saying stopping on warnings as well, but be able to ignore warnings.

We need to support this for both Controller based commands & queries as well as Model Bound commands in queries found in the Arc.Core project.

The default behavior should be that only Errors will stop an action to be performed. That being said, it should be possible to adorn an action to say "TreatWarningsAsErrors" but then have an explicit way of saying one ignores it.

This involves:

• Add a hook for validators to be able to add severity
• Add a hook for validators to be able to add state
• Add and honor attribute for actions saying [TreatWarningsAsErrors]
• Add a property on the generated frontend commands / queries saying if it has treatWarningsAsErrors turned on
• Add an optional / nullable boolean for the execute() method in the frontend for ignoring warnings.

Continue the work of this PR: #1789