WIP: New Tenant v1alpha2 version

[MaxFedotov]

@prometherion this is the first commit for #286. Adds new v1alpha2 Tenant spec

[prometherion]

I'm seeing some duplicated structs used also on v1alpha1, such as AllowedListSpec and AdditionalMetadata, just to name a few of them.

WDTY abstracting these structures in the domain package so we can reuse them across the two types? tl;dr; DRY principle

[MaxFedotov]

I was thinking about it, but then I checked https://github.com/Azure/azure-service-operator as an example, and they are copying structs between versions, not using abstract ones. And I think this approach had an advantage, because we will be able to modify them in future without breaking v1alpha1 CRDs.

Find out that copying structs between API versions is needed for correct DeepCopy func generation.
@prometherion I've updated this commit a bit (removed unused functions and packages from v1alpha1 and moved each v1alpha1 struct to a separate file). Can you please take a look one more time?

[prometherion]

LGTM