Split the feature pack module for better composability

[jmesnil]

the ai-feature-pack module contains both the "bits" that compose the feature pack as well as the definition of the feature pack itself.

While this works for simple feature pack, this lacks some flexibility to build advanced feature pack.
An alternative is to split this feature-pack into 2 modules:

• provision/common - contains all the bits (layers, modules, features)
• provision/feature-pack - contains the definition of the feature pack
  • this Maven module will keep the existing name wildfly-ai-feature-pack so that the structure change has no impact on the user experience