Implement missing validation attributes for exports

Validation attributes here: https://docs.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_functions_advanced_parameters?view=powershell-6#parameter-and-variable-validation-attributes

Many of these are likely necessary for certain types and situations. For example, if you need to pass an empty string to an `Update` cmdlet, you'll need `AllowEmptyString`. This decoration should be automatic by the autorest generator, but we don't have that logic implemented either. Similarly, `AllowEmptyCollection` would be needed if you wanted to provide an empty set of values to a cmdlet. Also, these attributes should be implemented anyway for those that want to use them in their customizations.