Adding AMBER force field

**Is your feature request related to a problem? Please describe.**
It is an additional force field which will be very useful for the refinement of parameters

**Describe the solution you'd like**
Adding the force field file as it was done in other examples

**Describe alternatives you've considered**
It is an additional alternative which can be useful for biomolecules

**Additional context**
Nothing to add

Start by locating the existing force-field files and examples referenced in the issue, then compare their format and integration points. Add the AMBER force-field file following those examples and verify that it is available for biomolecular parameter refinement.

Written by the indexing model from the issue text.