Globs for the checkpoints pointed to by checkpoint_prefixes. If the files
exist, collect their mtime. Both V2 and V1 checkpoints are considered, in
that priority.
This is the recommended way to get the mtimes, since it takes into account
the naming difference between V1 and V2 formats.
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Missing the information I need","missingTheInformationINeed","thumb-down"],["Too complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2020-10-01 UTC."],[],[]]