fix: Improve flag value resets between command executions

[avirtopeanu-ionos]

Currently, for flags that contain slices as values, the defaul CustomFlagResetBehaviour func would actually call Set which would append flag.DefValue to its previous value, rather than resetting to this default on command executions.

I found this nifty little interface SliceValue to which we can cast our pflag.Value. SliceValue exposes Reset() which we can use instead of Set() if the cast is successful.