[!379] cleanup the ParameterTree configurations of preconditioners

Merge branch 'feature/cleanup_preconditioner_configs' into 'master'

ref:core/dune-istl\>

### Summary

This MR adds missing documentation for ParameterTree arguments and replaces
repeated constructors by delegating constructors.

See merge request [core/dune-istl!379]

  [core/dune-istl!379]: gitlab.dune-project.org/core/dune-istl/merge_requests/379