helm mixin installs a hardcoded version of kubectl

[kurktchiev]

The version of kubectl being installed is:
a) hardcoded
b) should not be something this plugin installs

https://github.com/MChorfa/porter-helm3/blame/b6e6f54951eba5327c6070f3b3bd987793f0f56a/pkg/helm3/build.go#L86

[MChorfa]

This was done to prevent the mixin failling if the kubernetes mixin wasn't installed on the host machine. Will investigate a way to mitigate this