Feat adds content and header properties to CodegenResponse (!11046) · Merge requests · OpenAPI Tools / openapi-generator

Created by: spacether

Feat adds content and header properties to CodegenResponse These are needed

to allow responses to work for different response bodies dependent upon content type
to allow generated code to surface response header information and send correct accept headers to the server

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
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