ENH: fvOptions: refactor and extend effectivenessHeatExchangerSource

- rename effectivenessHeatExchangerSource -> heatExchangerSource
- introduce submodels:
  - effectivenessTable (previous behaviour)
  - referenceTemperature
- the referenceTemperature submodel uses a reference temperature
  which is either a scalar or calculated from a 2D interpolation
  table in order to calculate the heat exchange.