add `lb` open API specs

Seems lb API specs make openapi generator produce code which leads to rust compilation error.

https://developers.scaleway.com/static/88c7c88370da8e5a3316e5831e230183/scaleway.lb.v1.Api.yml

   Compiling scaleway_api_rs v0.1.0 (/Users/user/Code/scaleway-api-rs)
error[E0428]: the name `ips_api` is defined multiple times
  --> src/apis/mod.rs:78:1
   |
77 | pub mod ips_api;
   | ---------------- previous definition of the module `ips_api` here
78 | pub mod ips_api;
   | ^^^^^^^^^^^^^^^^ `ips_api` redefined here
   |
   = note: `ips_api` must be defined only once in the type namespace of this module

error[E0599]: the method `to_string` exists for enum `std::option::Option<&str>`, but its trait bounds were not satisfied
   --> src/apis/alert_subscribers_api.rs:237:74
    |
237 |     local_var_req_builder = local_var_req_builder.query(&[("name", &name.to_string())]);
    |                                                                          ^^^^^^^^^ method cannot be called on `std::option::Option<&str>` due to unsatisfied trait bounds
    |
   ::: /Users/user/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/option.rs:161:1
    |
161 | pub enum Option<T> {
    | ------------------
    | |
    | doesn't satisfy `std::option::Option<&str>: ToString`
    | doesn't satisfy `std::option::Option<&str>: std::fmt::Display`
    |
    = note: the following trait bounds were not satisfied:
            `std::option::Option<&str>: std::fmt::Display`
            which is required by `std::option::Option<&str>: ToString`

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0428, E0599.
For more information about an error, try `rustc --explain E0428`.
error: could not compile `scaleway_api_rs`

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