Improve and simplify config format

[Andre601]

I feel like the config is kind of bloated in some sections and could receive a improvement.

For example do I see no reason for having a lock option when the only goal for it is to have lock and unlock as options. This could just be an option for the action field and result in close + lock or open + unlock.

Another thing that could also be something to improve is the comment option.
This one could be changed to something like this:

comment: |-
  Hello,
  {{ content }}
  This is an automated comment created by a [GitHub Action](https://github.com/peaceiris/actions-label-commenter).
  Responding to or mentioning it has no effect.

The {{ content }} placeholder would then be replaced with whatever you defined in the corresponding body section of a label.

[peaceiris]

That looks very good! I will release both in the next major version.