[Enhancement] Add options to EspalomaTemplateGenerator to deploy different espaloma models

[kntkb]

The current implementation for EspalomaTemplateGenerator only accepts espaloma models that were jointly trained with charge losses which limits the use of different charge methods. Additionally, when the openmm system is created (here), there is no way to specify the forcefield used assign nonbonded parameters.

I think it would be great if we could have options to specify the charge method and the forcefield used to assign the nonbonded parameters.