ref(mongodb): Change grouping strategy for arrays and buffer

[0Calories]

Couple of changes here:

• Arrays in MongoDB queries were problematic for grouping, because any variant of the same query that has a different number of elements would result in an entirely new group being created. This resulted in high cardinality for a few orgs
• Removes the 'buffer' key-value pair from queries, since this is an under the hood mechanism which has very little relevance to the query itself. This causes unnecessary noise and makes queries hard to read, so we can scrub them out entirely

Examples

This would become:

"_id": {}

This would become:

"filter": {
	"_id": {
		"$in": ["..."]
	}
}