fix: always bind flags to env vars when configuring a command

Previously the `bindFlags` function that sets command flags based
on environment variables was only called the first time that the
`Config` function executes for a command.

In regular use, this isn't a problem because each time a user runs
a `metal` command, it's a separate execution.  However, this causes
problems in end-to-end tests because only the first test of each
subcommand runs the `bindFlags` function, so subsequent tests fail
because they do not look up the API token in environment variables.

This moves the `bindFlags` call so that it runs every time the `Config`
function runs, which enables tests to consistently set flags based
on environment variables.

internal/cli/root.go

@@ -137,9 +137,10 @@ func (c *Client) Config(cmd *cobra.Command) *viper.Viper {
 
  v.SetEnvPrefix(envPrefix)
  c.viper = v
- bindFlags(cmd, v)
  }
 
+ bindFlags(cmd, c.viper)
+
  flagToken := cmd.Flag("token").Value.String()
  envToken := cmd.Flag("auth-token").Value.String()
  // TODO: are we ok with this being configured by file too? yes?