Provide a way for the augmentation embedding process to pass in config defaults

[dmlloyd]

If there is information that the augmentation embedding process (Maven plugin, Gradle plugin, etc.) has which affects default configuration values (for example, app name, directory structures, etc.), it should be able to pass in an additional lower-priority configuration set (maybe as a config source/map, maybe as a file) to that process containing those values which would be overridable via system props, env props, and the normal application.properties file from the user.

Ideally we want 100% of build configuration to be processed by way of our config mechanism, rather than splitting it between our configuration and the build system's. This will also help to minimize the API as well.

[dmlloyd]

Directory structures includes things like input classes, output classes, and target directories.

[stalep]

With #1688 the plugins now properly send the correct resource directory to Quarkus. So most of the directories needed to build the runner/native are now properly set by Maven/Gradle.
There are still issues regarding correct test folders etc, these are now hard-coded in Quarkus. - we need to find a better way of doing that, atm it breaks testing with kotlin and if people use something different than the defaults.