Adds request body content data to allow multiple content types to be sent to servers

Created by: spacether

Adds CodegenMediaType and CodegenEncoding These are needed to allow request bodies to contain multiple content types and encoding definitions which are openapi 3.0.0+ features

One can read about these features in the openapi spec here https://github.com/OAI/OpenAPI-Specification/blob/main/versions/3.0.3.md#fixed-fields-10 in the content section.

This PR sets codegenParameter.content for:

• fromParameter (query, header, cookie, path parameters)
• fromRequestBody (request body params)

Not covered:

• form parameters because this code assumes that there is one codegenParameter to set content on. For that to work for form parameters, only one type object form parameter must exist. In the shared code today, the object is exploded into multiple form parameters, each which were properties of the object parameter.

@richardwhiuk

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 (5.3.0), 6.0.x
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.