Coulomb and Exchange function in RHF (C++ code) are missing

**Context** - To realize issue #1091, all HF methods need to have distinct functions for calculating the Coulomb and Exchange matrix in scalar basis. - Current RHF implementation (in [gqcp/include/QCModel/HF/RHF.hpp](https://github.com/GQCG/GQCP/blob/develop/gqcp/include/QCModel/HF/RHF.hpp)) calculates the Coulomb and Exchange matrix directly in the function of the Fock matrix. **Problem** Implementing the bindings stated in issue #1091 will lead to an error when calling these bindings for RHF as there are no Coulomb and Exchange matrix functions in the C++ code. **Solution** Remove the construction of the Coulomb and Exchange matrix from the Fock matrix construction and assign them their own function.