Replace mitchellh/* with maintained forks

[dbanck]

• Replace mitchellh/cli with hashicorp/cli
• Replace mitchellh/mapstructure with go-viper/mapstructure
• Replace mitchellh/go-homedir with ?

[radeksimko]

Replace mitchellh/cli with hashicorp/cli

👍🏻

Replace mitchellh/mapstructure with go-viper/mapstructure

👍🏻

Replace mitchellh/go-homedir with ?

I think we may be able to yank that dependency altogether. It needs double checking but since the library was born, there was some more work done in stdlib, specifically in os. Assuming it no longer requires CGO, the homedir.Dir() part could be replaced with os.UserHomeDir(). The stdlib still doesn't provide a convenience equivalent Expand() function but we could just copy these few LOC out into our codebase. 🤷🏻

There is still a risk of missing some edge cases described by Mitchell in mitchellh/go-homedir#20 (comment) but I think the cost vs risk here is in our favour given the size of our user base compared to e.g. Vagrant or Terraform (CLI), i.e. it's statistically less likely our users will run into these problems.