Save checkpoint version dirs as version_003 so that they sort lexicographically #20799
Description
Description & Motivation
Lightning saves checkpoint version dirs as version_3, version_21, etc. The problem with this is that when you do a listing, version_21 is between version_2 and version_3, making it easy to miss.
A simple solution, which is commonly used for these situations, is to name them version_002, version_003,... version_021, which solves the problem completely.
Note: If there's interest for this, this seems like a great first issue, and I'd be happy to write the patch.
Pitch
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Alternatives
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Additional context
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