Trusted domain API

[ChristophWurst]

nextcloud/server#29444 needs corresponding dev docs.

[ChristophWurst]

@nickvergessen will you make sure this is done for 23?

[nickvergessen]

The PR is in.
I wouldn't even know where I would expect such a documentation and also I find it rather niche, so not sure where to put it.

[ChristophWurst]

I would add a Security page to https://docs.nextcloud.com/server/latest/developer_manual/digging_deeper/index.html