feat: default commands & values from env vars

in gitlab-ci, you can define `DEFAULT_VALUE_` prefixed variables:

DEFAUT_VALUE_application_command: "my command"

which will get converted to

  command: my command

each value can additionaly be a json string and will then be parsed as such (if possible)

notice that any other values (from files, etc.) will take precedence over these variables
4 jobs for f/default-commands in 5 minutes and 29 seconds (queued for 2 seconds)