[CL] Use MPL to input amounts of ion exchanging species
This MR enables using the MPL to input the amounts (or molalities) of ion exchanging species as opposed to defining these quantities inside the
<chemical_system> tag, which is what is currently possible.
This MR partially resolves issue #3164 (closed) (after this, more MRs will be added to fully resolve the issue).
- Feature description was added to the changelog
- Tests covering your feature were added?
- Any new feature or behavior change was documented?