warn or fail if an application.yaml is provided without the quarkus-config-yaml dependency

[vsevel]

Description
If configuration is provided through a yaml file, but the quarkus-config-yaml has not been added, the configuration module will silently ignore the yaml file. it may take some time for the user to figure out that is what is happening, incorrectly thinking there is a bug in quarkus or smallrye config.
The proposition is to fail quarkus startup, or at least WARN the user that no properties file has been found, and a yaml file has been found,but will be ignored.

see also this discussion in the forum.

[ghost]

/cc @Ladicek, @jmartisk, @kenfinnigan, @phillip-kruger, @radcortez

[radcortez]

I'm wondering if we should just add the YAML source to the list of the default sources.

[vsevel]

@radcortez as yaml configuration looks more and more the standard nowdays, I completely agree.