Flag Referenced Enum as Enum - Issue 5676

Created by: rivancic

Fixes #5676 (closed) Referenced Enum is marked as Enum. There is additional flag on CodegenProperty#isInlineEnum that tells if enum is inline or referenced.

Sample Generation

At least one sample is failing to generate ATM.

Haskell issue

⚠️ Haskell sample project generation is failing. It has specific process for enums in HaskellHttpClientCodegen#toEnumName that throws NullPointerException when referenced schema isn't resolved. I might add a unit test for it in HaskellHttpClientCodegenTest and try to fix it, while I would rather delegate this to someone more experienced with this part of logic in Haskell.

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 (6.1.0) (minor release - breaking changes with fallbacks), 7.0.x (breaking changes without fallbacks)
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