Apply new checkbox style to admin settings

[Henni]

fixes #19724

cc @jancborchardt

[MorrisJobke]

cc @owncloud/designers @PVince81

[MorrisJobke]

Tested and works 👍

[PVince81]

Code looks good 👍

[jancborchardt]

Isn’t this also something which we should backport to 8.2 then? cc @karlitschek @cmonteroluque because atm in some places we have the new checkboxes, and in some we don’t, which is not very elegant.

[karlitschek]

yes. backport please. honestly i'm surprised that this wasn't fixed a long time ago

[jancborchardt]

Yeah, I was also confused pulling the new code coming back from vacation. ;) But great work @Henni! :)

[PVince81]

the explanation is simple: the initial fix touched ALL the checkboxes that have a "label" tag. But since some apps didn't have them, their checkboxes were broken. So the initial fix was not acceptable due to app breakage and was reverted, and now checkbox styles need to be opt-in. So all checkboxes that used to work with the old approach would need to be adjusted directly, and some might have been missed during the second pass.
See #19304

[jancborchardt]

@Henni can you rebase so we can merge and backport? :)

[Henni]

@jancborchardt done

[nickvergessen]

@Henni please send a backport Pull request against stable8.2

[Henni]

@nickvergessen I'm not completely sure how to do this, but I'll try.

[nickvergessen]

git checkout stable8.2
git checkout -b backport-19744
git cherry-pick bf722d9
git push origin backport-19744

And then send a PR against stable8.2