Detect and suggest models and layers in a feature pack during features add operation

[spyrkob]

When user enters prospero feature add --fpl <FEATURE:PACK> --layers <TAB>, prospero should list layers available in that feature pack. Similarly for --model parameter.

Requirements:

• detect and list available layers and models in a feature pack user selected using --fpl argument
  • see FeaturesAddActiongetAllLayers to check how to analyze the feature pack
• add an completionCandidates on the layers and modules fields
  • NOTE: the completionCandidates have to have a static way to initialise and retrieve the feature pack name, see Dynamically generate completion candidates at runtime remkop/picocli#837

Test/reproduce setup:

• install WildFly server using prospero
  prospero install --fpl wildfly --manifest examples/wildfly-29.0.0.Final-manifest.yaml --dir wildfly
• create a datasources FP manifest (e.g. for datasources FP) and add it together with repositories as a new channel
  follow https://www.wildfly.org/news/2023/11/27/prospero-add-feature-pack/#creating-feature-pack-channel
• try to add the Datasources feature pack -
  • start entering prospero fp add --fpl org.wildfly:wildfly-datasources-galleon-pack --layers
  • hit TAB key to see candidates
    • nothing will happen
    • after implementing the completion layers supported by the feature pack will be displayed