Fixed scala-sttp generator (!11949) · Merge requests · OpenAPI Tools / openapi-generator

Created by: chrisbartoloburlo

Fixed multiple bugs present in the scala-sttp generator:

The generated requests were using Nothing instead of Any as the capability parameter (as mentioned also here). Fixed by changing (api.mustache) to use Any.
When the responses inside a swagger file were specified as default, the code generated was erroneous. In particular, the returned value used to be generated as asJson[Unit] which caused a matching error at runtime. Fixed by updating the return value to asEither(asString, ignore) and the corresponding return type of the generated function as indicated by the sttp contributors here.
3bc4895 fixes imported libraries in the generated api package. Libraries such as Set used to be imported as org.openapitools.client.model.Set, however Set was not generated as a model. Now it imports the Scala standard library scala.collection.immutable.Set instead.

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. @chameleon82