Generates random secret with specified length.

$ mix h.gen.secret --length 64

By default, mix h.gen.secret generates a key 64 characters long.

The minimum value for length is 15 unless force request!

Links(based on Plug.Crypto)

• https://hexdocs.pm/plug_crypto/Plug.Crypto.html
• https://github.com/phoenixframework/phoenix/blob/main/lib/mix/tasks/phx.gen.secret.ex
• https://github.com/phoenixframework/phoenix/blob/main/lib/phoenix/token.ex