`atlantis generate repo-config` should support automatically generating `when_merged` configuration

### Describe the Feature

Currently `atlantis generate repo-config` uses a predefined set of strings to put into the config key for `when_modified` for an atlantis project. This has one major downside: Atlantis just scans the component directory for changes files which does not include changed files `/stacks`. If you have only a config change in the stack folder atlantis does not recognize that it need to plan this project.

### Expected Behavior

`when_modified` should be completely generated with all files under the component itself and corresponding files in `/stack`.

### Use Case

Configuration change in `/stacks` folder

### Describe Ideal Solution

see expected behaviour.

### Alternatives Considered

_No response_

### Additional Context

_No response_