Display Only Unique Warnings/Errors w/ File Count

[bendhouseart]

Putting this here before I forget, but came across an older dataset that is valid, but with the improvements to the validator now displays itself as having 10's of thousands of warnings. I'm thinking something like this for the json output for starters:

{
    "code": "SIDECAR_KEY_RECOMMENDED",
    "subCode": "GradientSetType",
    "severity": "warning",
    "rule": "rules.sidecars.mri.MRIHardware",
    "issueMessage": "Field description: It should be possible to infer the gradient coil from the scanner model.\nIf not, for example because of a custom upgrade or use of a gradient\ninsert set, then the specifications of the actual gradient coil should be\nreported independently.\n",
    "count": 620
}

I feel like the count is a bit less intimidating than a terminal screaming at you 620 times.

Mostly putting this here so I don't forget about it.

[rwblair]

So schema results have a grouping api. Example of groupby in action for normal output:
https://github.com/bids-standard/bids-validator/blob/main/src/utils/output.ts#L46

Will need to hook new flag in/before here depending on where you want to do the group by munging:
https://github.com/bids-standard/bids-validator/blob/main/src/main.ts#L39