Add a CLI to create objects supported by SecretGen controller

**Describe the problem/challenge you have**

YAML is hard to remember. Every time I want to create an object of this controller, I have to look at something I've done before, or come here to read the docs.

**Describe the solution you'd like**

A CLI, similar to `kctrl` (much Kudos for `kctrl` 👏 ), that allows to create some, or all, of the objects supported by this controller. As an example, I would like to add a `SecretExport` by doing:

```console
secgenctl secretexport create my-secret-export -n my-super-secret-namespace --to-namespaces '*'
```

This is an example, the idea is to support create/list/get/delete operations using this CLI for all objects.

**Anything else you would like to add:**

To my mind is a lot easier to remember CLI commands than YAML structures. A CLI can provide a `--help` option, and that's faster than opening a browser and navigating to the docs of this controller.

I'll be happy to contribute a PR!

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