Services.properties value for metadata-providers in default file from install

[Rod Widdowson]

> So, actually, I see you're just talking about the *property*. I think I
probably
> was thinking that we should default to not making the addition of new
> metadata sources a totally automated operation and that if people wanted
to
> manage metadata that way, they could always just change the setting.

FWIW: That’s my memory too.
 
> I don't think it was a deeply held opinion or anything.
Ditto.