DATACMNS-557 - Added support for custom implementations to CDI infrastructure.

The CDI extension now discovers a custom implementation class similarly to the detection when using Spring Data in a Spring container. Extracted the custom implementation detection for re-use. The CDI extension discovers the potentially available bean and hands it to the CdiRepositoryBean for further usage.

Implementations should implement the extended variant of the create(…) method we introduce with this commit to be able to forward the resolved custom implementation bean.

Original pull request: #92.
DATACMNS-557 - Polishing.

Renamed CdiRepositoryConfigurationSource to CdiRepositoryConfiguration. Turned anonymous inner default implementation into dedicated enum to avoid repeated instantiation.

Changed the CdiRepositoryBean to rather take a Bean instance of the custom implementation instead of the resolved object to make sure both instances (the custom implementation and the repository proxy) are instantiated at the same time.

Fixed imports. Some early returns to avoid unnecessary nesting.

Adapted architecture description to allow CDI module accessing the configuration module.

Related pull request: #92.