[rust] basic oneOf support

Created by: nshaaban-cPacket

Generates oneOf enums.

openapi: 3.0.1

info:
  version: "1.0.0"
  title: rust one-of fix
paths: {}
components:
  schemas:
    Foo:
      x-one-of-name: Foo
      oneOf:
        - type: object
          required:
            - field_one
          properties:
            field_one:
              type: string
            field_two:
              type: string
        - type: object
          required:
            - field_three
          properties:
            field_three:
              type: number

Expected behavior: Able to fill in struct fields in such a way that creates a valid request Actual behavior (on master): Impossible to fill the struct Foo to make it a valid schema (as BOTH required fields (field_one and field_three) are required to be filled in rust, yet the openapi schema only allows one or the other to be set. Actual behavior (on this PR): able to fill fields by using the corresponding variant on the enum Foo.

use super::FooOneOf;
use super::FooOneOf1;

#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
pub enum Foo {
    FooOneOf(Box<FooOneOf>),
    FooOneOf1(Box<FooOneOf1>),
}

Known Limitations

• oneOf and properties on the same level.
• model.mds still need to be updated to match the new enum scheme
• (existing) oneOf and discriminator where mapping is not explicit

Related issue

https://github.com/OpenAPITools/openapi-generator/issues/9497

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package 
  ./bin/generate-samples.sh
  ./bin/utils/export_docs_generators.sh

  Commit all changed files. This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master. These must match the expectations made by your contribution. You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*. For Windows users, please run the script in Git BASH.
• File the PR against the correct branch: master (6.3.0) (minor release - breaking changes with fallbacks), 7.0.x (breaking changes without fallbacks)
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

@frol @farcaller @richardwhiuk @paladinzh @jacob-pro