Improve Spring integration

Improve Spring integration by supporting a typical Spring Enablement annotation:

@EnableTamayaConfig

If added to a Spring @Configuration this enables and loads Tamaya as a Spring configuration backend (PropertySource). By default Tamaya overrides existing Spring configuration and also enables Tamaya Configuration injection on Spring beans.

This can be customized by configuring Tamaya integration on the annotation, e.g. as follows:

@EnableTamayaConfig(disableTamayaInjection = true)
@EnableTamayaConfig(extendOnly = true)