Gradle: handle dependencies exclusion

[Aurélien Mino]

Example use case: spring-boot-undertow jhlite module needs to exclude dependency spring-boot-starter-tomcat.
Currently the generated app with spring-boot-undertow starts with tomcat :(

[Aurélien Mino]

@pascalgrimaud : bounty claimed https://opencollective.com/generator-jhipster/expenses/199151

[Pascal Grimaud]

@murdos : approved