Request: Support wildcards in `--namespace`

[tonglil]

Would like to re-open #339 to natively support wildcard/globbing namespace.

I would prefer to be able to specify --namespace my.namespace.* natively, rather than first parse with bash and then pass in many --namespace flags.

This is especially needed given the existence of the --combine flag.

My rules are organized like:

policy/
├── data
│   ├── combined
│   └── simple
├── k8s
│   ├── combined
│   │   ├── deployment
│   │   ├── hpa
│   │   └── pod
│   └── simple
│       ├── deployment
│       ├── hpa
│       └── pod
└── terraform
    ├── combined
    └── simple

I would like to be able to execute rules in combined namespaces only with the --combine flag, and the simple namespaces without it, like so:

 # data and terraform namespaces only
conftest test target/ --namespace *.simple
conftest test target/ --namespace *.combined --combine

 # k8s only
conftest test target/ --namespace k8s.simple.*
conftest test target/ --namespace k8s.combined.* --combine