Reducing common structs types or https://github.com/kube-rs/gateway-api-rs/issues/38

[dawid-nowak]

This approach aims to simplify the types and eliminate redundant ones. The approach works as follows:

1. We scan generated files and find similar items (structs or enums). Two structs are considered to be similar and processed further if their fields are exactly the same. The same method applies to the enums.
2. Once all similar structs and enums have been found, then we try get the name that will applied to similar structs from a file.
3. Once the new type names are settled we change the generated code and add a new file with the reduced types "common_types.rs"

We follow this process in phases:

1. In Phase 1, we only look at the structs with fields which are built from simple types (String, u32, u64)
2. In Phase 2, we also look at the structs with fields that have been changed in Phase 1
3. and repeat

Problems:

1. The documentation is stripped since the same type could be used in many different locations