[REQ] maven plugin: remove `generateApis` and `apisToGenerate`

Problem

The openapi-generator-maven-plugin currently has 3 different options to influence which Apis will be generated: generateApis, apisToGenerate and globalProperties.apis. OpenAPI Generator itself only knows about globalProperties.apis. generateApis and apisToGenerate work by openapi-generator-maven-plugin modifying globalProperties.apis.

Some disadvantages with that:

• Having 3 options where 1 would be sufficient adds complexity and confusion.
• This led to bugs in the past: https://github.com/OpenAPITools/openapi-generator/issues/4506
• Setting generateApis=false doesn't actually guarantee that API are not generated. (Specifically when also setting generateModels=false and generateSupportingFiles=false.)
  related: https://github.com/OpenAPITools/openapi-generator/issues/16257

Proposal

Therefore I propose to remove the options generateApis and apisToGenerate. All the available functionality is accessible by setting globalProperties.apis accordingly.

The same probably also applies to globalProperties.models and globalProperties.supportingFiles.

If this proposal is accepted by a maintainer, I'd be open to work on a PR.

Start by reviewing the openapi-generator-maven-plugin handling for generateApis and apisToGenerate, then inspect the related tests and plugin documentation. Confirm how globalProperties.apis currently provides the same functionality and define done as removing the two options without losing supported API-selection behavior; the possible models and supportingFiles changes need maintainer confirmation.