[mrm-task-stylelint] Support stylelint-config-prettier when there is prettier

[riywo]

Similar to mrm-task-eslit, we can add stylelint-config-prettier to .stylelintrc when there is prettier.

One caveat is the default prettierPattern doesn't include .css. So, it might be good to check whether there is also .css in the pattern.

Or, additional option (like extraExtends?) for this task can be also better because the customers can control.