[CBBM] Not able to map collections due to missing system collection check

This is related to: MB-58085

What's the issue?
When mapping of data is used, we check the cluster manifest containing the current bucket and its scopes and collections before we start the restore of the backup bucket. This check contains a step that checks for the collections in a scope in the cluster using the scope ID from the backup, if the collection does not exist cbbackupmgr exits stating that it does not exist as the error mentions:

Error restoring cluster: 'Bucket1.scope-nour.c1' does not exist on the target cluster; you must exclude it (-include-data/-exclude-data)

This should not be the case, this step should be checking if the collection does not exist AND it’s a system collection to indicate whether using this bucket mapping will result in attempting to transfer a system collection on a cluster where it has been deleted. We are currently not checking for this system collection and erroring out.

What's the fix?
Add a system collection bool check in this if statement with the nil collection check.