Turn NOGW tendency into a callback

[nefrathenrici]

Non-orographic gravity wave tendency should not be called every timestep, it should be a callback instead.

We should also provide the u_forcing and v_forcing quantities as diagnostics

[charleskawczynski]

I'm just curious, why is this?

[nefrathenrici]

These are some minor improvements to take care of before updating the parameterization to match the GFDL code. This is not high priority, but I plan on getting to it next week.

[szy21]

I'm just curious, why is this?

Adding nonorographic gravity wave in AMIP results in ~20% reduction in SYPD. We can further improve the performance, but we don't really need gravity wave every time step, so turning it into a callback and calling it e.g. every hour is a straightforward solution.