Add a kwarg to avoid POTCAR checking in correction scheme

[Andrew-S-Rosen]

This mainly concerns the MaterialsProject2020Compatibility scheme, so I'm CC'ing @rkingsbury here.

https://github.com/materialsproject/pymatgen/blob/dcc4576fb8fb89b7adc2f31158654392348e6498/pymatgen/entries/compatibility.py#L941-L944

The above codeblock checks the POTCAR symbols when getting a correction. While this is a very useful tool, I don't know that it should be required to obtain a correction. For instance, my entry objects don't have any data about POTCARs in them, but I can't get the corrections without commenting out this codeblock.

@rkingsbury: Are you opposed to me adding a kwarg check_potcar to get_adjustments() or to __init__ to optionally bypass this check? I feel like the difference between this and check_potcar_hash=False is potentially confusing though. In the case of check_potcar_hash, the POTCARs are still check but just their symbols and not the hash itself. Any suggestions