[Kotlin][gradle] Issue #8255 fix (inputSpec param not accepts URL)

Created by: Orachigami

Fixes: https://github.com/OpenAPITools/openapi-generator/issues/8255

Implemented @joschi recommendation with the additional parameter

Maybe splitting the input specification location into local specs and remote specs would make sense?

Related PR: https://github.com/OpenAPITools/openapi-generator/pull/9192

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