Added API for context aware config resource injection.

[niekraaijmakers]

Makes the following possible:

`@model(adaptables = {SlingHttpServletRequest.class, Resource.class}, defaultInjectionStrategy = DefaultInjectionStrategy.OPTIONAL)
public class SampleModel {

@via(type= ContextAwareConfigResource.class, value = "config")
@ValueMapValue
private String propertyTest;

public String getPropertyTest() {
return propertyTest;
}
}`

Use via to point to context aware config resource, to inject valuemap values.
Tested it locally and works fine with latest versions.
What do you think?

[stefanseifert]

there is already an a JIRA ticket for this topic https://issues.apache.org/jira/browse/SLING-7256
the open questions is whether this integration goes in to

• a) caconfig api/impl or
• b) models api/impl
• c) a separarate module

i would prefer b) or even c).