Add option to automatically rebuild merge plan

[samdark]

Proposed new feature or change

Add an option to automatically rebuild the merge plan. If it is turned on, yii-config-rebuild is not required since the plan is rebuilt automatically. By default, it should be turned off.

[vjik]

Merge plan builder requires Composer instance, that available in composer commands. See:

config/src/Command/RebuildCommand.php

Line 28 in 39800f6

new MergePlanProcess($this->requireComposer());

Is there a way to get it outside of the composer command?