Today the basic node settings like `node.data` and `node.master` can't really be fully validated
since we allow to specify custom user attributes on the node level. We have to, in order to
support that, add a wildcard setting for `node.*` to let these setting pass validation.
Instead we should require a more contraint prefix like `node.attr.` that defines a namespace
that is reserved for user attributes.
This commit adds a new namespace for attributes in `node.attr`.
Closes#17280
8b075dbb75