input: Secret type support

[kamilsk]

Motivation: there is no way to define this type of value.

Example

• https://github.com/octomation/maintainer/blob/af46d826f7c070347b26fa46efee6dbdee4f8be3/internal/command/github/root.go#L22
• https://github.com/octomation/maintainer/blob/af46d826f7c070347b26fa46efee6dbdee4f8be3/internal/config/tool.go#L18

PoC

set := command.PersistentFlags()
set.Secret("token", "", "personal access token")