fix(SetupCheck): Properly check public access to data directory

fix(SetupCheck): Properly check public access to data directory

When checking for public (web) access to the data directory the status is not enough
as you might have a webserver that forwards to e.g. a login page.
So instead check that the content of the file matches.

For this the `.ncdata` file (renamed from `.ocdata`¹) has minimal text content
to allow checking.

¹The file was renamed from the legacy `.ocdata`, there is a repair step to remove the old one.

Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>