feat(helm): prompt for password with helm repo add
feat(helm): prompt for password with helm repo add

Previously in Helm 2, 'helm repo add' would prompt for your password if
you only provided the --username flag. This helps prevent someone's
credentials from being logged in their shell's history, from showing
up in process lists, and from being seen by others nearby.

Closes #7174

Signed-off-by: Jack Weldon <efd5ded1430890740d406234dc6930691e3a2f92@gmail.com>

michelleN/deployment-manager,bacongobbler/helm,michelleN/deployment-manager,helm/helm,bacongobbler/helm,helm/helm,adamreese/helm,michelleN/deployment-manager,adamreese/helm,michelleN/deployment-manager