Ref https://github.com/helmfile/helmfile/discussions/593
* implemented --reset-values flag overriding .helmDefaults.reuseValues=true
* tests for --reset-values flag
* fixed pkg/app tests
* added tests for both reset & reuse flags given
* added appendValuesControlMode method for --reuse/reset-values flag processing
* updated code comments & docs
Signed-off-by: Karol Ossowski <k@koralsky.pl>