Move this project and generate result to ESM

There's one big problem.

• We need to remove namespace from the generated results. In that case, how do we guarantee the uniqueness of the output type names?

via. https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c#how-can-i-make-my-typescript-project-output-esm

One easy option would be to prefix every type / interface name with the namespace name. So for example

namespace Responses {
   export type BadRequest = any;
}

becomes

export type ResponsesBadRequest = any;

That would not necessarly guarantee uniquenesss but should work for most setups.

Thanks for the good ideas. 👍 The name will be much longer, but I think I can guarantee uniqueness.