ENH: buoyancyTurbSource: add a new fvOption

    Applies sources on turbulent kinetic energy (i.e. `k`)
    and either turbulent kinetic energy dissipation rate (i.e. `epsilon`)
    or specific dissipation rate (i.e. `omega`) to incorporate effects
    of buoyancy on turbulence in incompressible and compressible flows.

    See buoyancyTurbSource.H for details.