Provide methods to retrieve the CacheKey parameters

Currently, it's not possible to retrieve the parameter values composing the CacheKey (generated by JCache interceptors). For that, we could introduce two interfaces.

• SimpleCacheKey<T> used when only one parameter is used as key. This interface could add the following method T getValue()
• ComposedCacheKey used when the key is composed by more than one parameter. This interface could add the following method Object[] getValues()

Here, we need to ensure that we are compliant with the specification.