Improvements + removal of go anti-patterns

[Mzack9999]

• The type StringSlice should be vaporized and revert back to []string - the reference implementation should accept as destination var the basic []string go type, just like in https://github.com/spf13/cobra (ref https://pkg.go.dev/github.com/spf13/pflag?utm_source=godoc#pkg-index). Normalization options should be pluggable variadic arguments (eg. WithLowerCase(..), WithUpperCase(..), etc), it's up to the caller to set the wanted options.
• Only a very limited subset should be kept, such as FileToStringSlice which supports automatically reading from file
• All the implicit normalization (spaces, "' in comma separated strings) implicit logic must be removed and handled with only caller defined options (this is the source of intinite issues with various XXXTypeHolder wrappers in nuclei codebase)