Support pass registration for executors of specification languages

[fwendland]

Executors for specification languages should be able to register passes with the CPG.

For example, the executor for MARK requires two additional passes (IdentiferPass and EdgeCasePass). These need to be added as CPG specific configurations. However, other executors may not depend on these passes.

Thus, there should be some facility that an executor can register (additional) CPG passes.