Allow specific keys to be excluded from `flatten`

[benjamin-awd]

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Use Cases

We often perform selective flattening for our payloads, meaning that we often need to exclude certain keys during the flattening operation. Currently this requires a somewhat verbose save/restore dance:

metadata = del(.metadata)
tags = del(.tags)

. = compact(flatten(., "_"))

.metadata = metadata
.tags = tags

This is also useful for downstream consumers that do not necessarily want to flatten specific fields and instead want to store them within a JSON record/column.

Attempted Solutions

No response

Proposal

Add an optional except parameter to flatten that accepts an array of key names to exclude from flattening:

. = compact(flatten(., "_", except: ["metadata", "tags"]))

Keys matching the except list would be preserved as-is while everything else is flattened normally.

References

No response