Rename "language" to "generator-name" in cli and maven-plugin

Created by: jmini

On the long term we might want to offer an other way to select the targeted generator.

Probably with multiple switches (to be defined more precisely):

Examples:

cli -type=client -language=kotlin
cli -type=server -language=kotlin -framework=ktor

A first move that we could do now with our first release is to rename the term “language” with “generator-name“ in the maven Plugin and in the CLI.

We might support them both options for backward compatibility, but with a warning explaining that “generator-name“ should be preferred.

What are the opinions?