Proposal for ash_postgres.squash_snapshots mix task

[vonagam]

The idea is simple - a task to clean up snapshots and remove all but last ones.

With usual flags --check, --dry-run, --snapshot-path and --quiet. Plus --into flag that can take first, last or zero and determines the name for a remaining snapshot (first, last are self-explanatory, zero means name with fourteen zeros).

The additional bonus of such task is that its usage (with --into first or --into zero and --check for CI) can help with problems currently present when multiple branches generate migrations and then get merged. The problems that #75 should fix. But unlike operations this task can be implemented quite trivially (and squashing will still make sense to have even after operations are in place).

This is a thing that I had proposed on Discord relatively recently. Just want to confirm the judgement on it. No pressure from me, if it does not fit in the official package I might do it as a separate package then.

[zachdaniel]

I'm happy to see the task exist 👍 It will be entirely different once operations exist, but the concept wouldn't go away.