Configuration validation: consider version information before adding fields

[WardBrian]

Currently, we can't tell the difference between a key that was deleted and one that never existed. This means someone e.g. deleting a special uniform in the colors json would just have it added back for them. We could instead gate this adding back on the config being sufficiently old

Originally posted by @WardBrian in #740 (comment)

[ty-porter]

Once we implement this I'm open to removing allow_special_uniforms from the team colors config. Should be very straightforward as the config validator will remove the key in any custom config for us.

[jc214809]

you could prompt the user about this