[Scala][sttp] various bug fixes (!12254) · Merge requests · OpenAPI Tools / openapi-generator

Created by: smiklos

There are a couple of issues with the sttp codegen support.

enum should not be used as it will be a reserved keyword -> changed this in JsonSupport
Enums were completely missed and not generated at all -> Fixed
AnyType was added as value type for maps where the schema type is object. These should be encoded as a json library specific json value (personal opinion)
URI serializer is added to support URI as well.

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.
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