SALTO-1242 - Add dedicated command for re-generating the cache

[netama]

Add option to recompute the nacl file cache separately from deploy/fetch, based on @roironn 's suggestion.
This can be useful for speeding up the VSCode extension on slow machines, allowing it to run quicker reference lookups without requiring heavy blocking computations.

This is added initially as an additional flag under the clean command - we may want to revisit this later.
This can be combined with any other clean flag except for cleaning the cache.

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Release Notes:
Add option to re-generate the file cache as part of the salto clean command

[coveralls]

Coverage increased (+0.004%) to 94.436% when pulling 60de7be on netama:feature/SALTO-1242-regenerate-cache into 91e8c85 on salto-io:master.