Cleanup extrapolator configuration for ITk

Cleanup extrapolator configuration for ITk:

• avoid separate configuration fragments
• make the tool private and configure it as public with clients if needed
• also cleanup CaloExtensionBuilderAlgCfg as the extrapolator was the only big dependency

A companion to !48415 (merged).

/cc @christos @tstreble @npetters @pagessin @lgagnon @nstyles