Records grouping

[mathemancer]

Related to #3690

Adds a number of SQL functions that produce groupings of records when required. The grouping object submitted should have the keys columns and (optionally) preproc.

The resulting grouping object will have the keys columns, preproc, and groups.

The values associated with each of these keys are the same as in the REST API.

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The new functionality is documented, and if the documentation is insufficient to understand how this works, or the needed request format, please request an improvement.

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[mathemancer]

@Anish9901 This can be reviewed, I've just marked it as a draft since it depends on #3708, and should not be merged until after that one.

[Anish9901]

This looks great @mathemancer, I've requested some minor changes after which this can be merged.

[Anish9901]

@mathemancer we should probabaly also metion somewhere that ordering is nessasary for grouping to work as intended.

[mathemancer]

Review comment so my pending comments will show 💩 💩

[mathemancer]

@mathemancer we should probabaly also metion somewhere that ordering is nessasary for grouping to work as intended.

I'm not sure. The REST API works the same way, and (in my mind) these operations should be thought of separately. There are other possible UIs that would (for example) just annotate each row with its group ID and/or count.