Add support for api groups in Scalar

[Dyskal]

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

Swagger UI and Scalar supports api groups / multiple sources / .... But only the springdoc swagger-ui package actually implements it.

Describe the solution you'd like

Support for multiple sources in Scalar.

How should it be implemented

The method AbstractScalarController#getDocs(String requestUrl) should modify the CONFIGURATION object with a sources array built the same way as the swagger-config endpoint in swagger-ui package is. Thanks