Add Support for .kubevalignore file

Hi there,
a tool like this - that can be used accross a lot of different repositories - would benefit in its flexibility by a lot if we could configure it to ignore specific files even if they are in the recursive list of resources.

Example scenario we have a repository with a lot of k8s files and this is fine but now we got additionally a kustomize patch and this is where it breaks.
```bash

echo "# Kubeval - Checking dev/"
kubeval --ignore-missing-schemas --directories ./dev || exit 4
```
Ideally we would like to add a ".kubevalignore" with something like this:
```bash
# Match only directories containing kustomization or overlay
*kustomization*/
*overlay*/
```

This way we can ignore the patches and other kustomization that is not a valid manifest.