Is your feature request related to a problem? Please describe.

The Gradle plugin openApiValidate task accepts a --input CLI flag to pass the path to the API spec. This is useful where the code generation is happening in a separate project to the development of the API spec. The openApiGenerate task does not, which makes it hard to specify the location of the spec for code generation.

Describe the solution you'd like

The openApiGenerate task to accept a --input flag

Describe alternatives you've considered

Passing properties to Gradle. However this interferes with IDE Gradle integration (eg: Android Studio), as, if the property is not found Gradle throws an error. There is currently no way to specify additional properties to the IDE for Gradle integration.

A CLI flag allows the user to pass the location of the spec to the task, without having to use more complex trickery.

Additional context