feat(stackable-versioned): Re-emit and merge modules in versioned modules

[Techassi]

Part of stackabletech/issues#642

This PR allows users to define modules in the versioned module, which allows composition of imports which then produces easier to consume imports in downstream code.

Example

// In crate/crd/mod.rs

#[versioned(
    version(name = "v1alpha1"),
    version(name = "v1")
)]
mod versioned {
    mod v1alpha1 {
        pub use crate::crd::oidc::v1alpha1::*
        pub use crate::crd::tls::v1alpha1::*
    }

    struct Foo {
        bar: usize,
    }
}

[NickLarsenNZ]

LGTM. I'll leave it up to you if you introduce the error handling now or later (which will technically be a breaking change).

[NickLarsenNZ]

LGTM