Periodically purge non-existing extensions #167
Description
Now that we don't track maxMissingTimes (#139), we don't purge extensions that were missing a specified number of times. Therefore, extensions removed from the VS Code Marketplace and Open VSX may stay in the cache arbitrarily long.
We need a way to periodically purge such extensions. Below is a sketch of the solution.
Add a CLI parameter to the updater (Haskell program) to conditionally remove all missing cached info after fetching configs. The parameter argument should be a cron expression. When the current date matches this expression, missing info will be removed.