Dispatch updates as patches to allow for modifications

[ChristophWurst]

The workflows we distribute through this repo should be templates, not copies. Apps should have the ability to fine-tune them to their needs. Therefore it's tiresome if we always get PRs with fully replaced files where we have to hand-pick our changes on top of the new version. Example: nextcloud/contacts#2620 (comment).

So I'm proposing that ideally the dispatching of updates should apply them as patch, so that only the changed parts in this central repo are applied on the potentially modified copies. There will be conflicts where modifications are overwritten by updates, but in the happy case there is nothing to merge manually.