[Docs] Catalog promotion label customization

[AdamKasp]

Q	A
Branch?	master
Bug fix?	no
New feature?	yes
BC breaks?	no
License	MIT

should be merged after https://github.com/Sylius/Sylius/pull/13389/files

[Zales0123]

If we need to override so much code just to customize the label... it seems that something is wrong :( Maybe we can extract some template and make it simpler and more generic?

[CoderMaggie]

Let's maybe rename the file to be simply:
docs/cookbook/promotions/catalog-promotion-labels.rst

[GSadee]

The base of this pull-request was changed, you need fetch and reset your local branch
if you want to add new commits to this pull request. Reset before you pull, else commits
may become messed-up.

Unless you added new commits (to this branch) locally that you did not push yet,
execute git fetch origin && git reset "catalog-promotion-label-customization" to update your local branch.

Feel free to ask for assistance when you get stuck 👍

[GSadee]

Thanks, Adam! 🎉