Fix interpolation of %args% and make default value possible #29

Fix command parsing:
For the host level command, args parsing is currently skipped, need to fix this. Also make it regex replace with global flag.

Add default args
An action might provide "args" string value that is used as fallback when interpolating %args% from "command". Consider below composer action:

"actions": {
   "composer": {
      "args": "install --prefer-dist --no-scripts",
      "command": "%action% %args%"
    }
}

As per this default, running dopr composer will actually run composer install --prefer-dist --no-scripts but running dopr composer update will run composer update in the underlying service container