Add --clone-shallow-since-days option for the locker

[urbanikb]

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What

Add option to configure clone_shallow_since_days option that's already supported in the locker class.

Why

Our evidence locker is too large to fully clone locally and it makes it extremely difficult to work with the prune command without this flag.

How

• Add a new command-line argument --clone-shallow-since-days to the _CorePruneCommand class.
• Update the _get_locker method to accept an additional parameter clone_shallow_since_days.
• Pass the clone_shallow_since_days attribute of the PruneLocker instance if the clone_shallow_since_days argument is provided when creating the locker.

Test

• Executed the prune command with no issues:

$ prune push-remote https://(private repo) --config-file ./prune.json --clone-shallow-since-days 1
This is an official run.  Remote locker will be updated...
Cloning local locker for https://(private repo).  Depending on the size of your locker, this may take a while...
Locker has been cloned...
Local locker location is /var/folders/zb/6h4wth3j3g3561s518fcy70r0000gn/T/prune

Evidence (private repo file).json removed by boris.urbanik@ibm.com, tombstone applied...

Evidence (private repo file).json removed by boris.urbanik@ibm.com, tombstone applied...
Remote locker was updated...
Removing local locker...
Local locker has been removed...

Context

• Add a shallow clone option #9