feat(tactic/apply_rules): allow apply_cfg argument (#3538)
This allows passing an `apply_cfg` argument to `apply_rules` (and simplifies the configuration argument to `solve_by_elim`).
This is prompted by the desire to try using `apply_rules` with `md := semireducible` when working on the `continuity` tactic.
Co-authored-by: Scott Morrison <scott.morrison@gmail.com>
