Store the MP `ValidationDoc` in the output of MP recipes

[Andrew-S-Rosen]

What new feature would you like to see?

https://github.com/Quantum-Accelerators/quacc/blob/a1101d7a344e993f26bb5a7037f6fb45f9b395ba/src/quacc/recipes/vasp/mp.py#L113

Here, we run the MP validation scheme to log a warning if the results do not match MP compatibility. However, this is not stored anywhere in the output. We should ensure this gets stored in the output schema, but we also want to make sure it makes it into the resulting DB so it probably needs to be its own dedicated schema.