Add permission overwrite warning text to creation of WebDAV share

When you edit permissions in Storage -> Pools and check "Apply permissions recursively", you are warned that it might make data inaccessible.

When you create a WebDAV share, "Change User & Group Ownership", which overwrites the permissions of all the contents the share, is checked by default and does not warn you that it might make data inaccessible. It should display the same data inaccessible warning that "Apply permissions recursively" does. This makes it easy for new users to accidentally overwrite permissions and lose access to data.

I am a new FreeNAS user, and this exact thing happened to me.