The "subdomain" label is redundant, to the extent it's even
accurate -- this is really just the URL we want to display,
which may or may not involve a subdomain. Similarly "external".
The former `external_api_path_subdomain` was never a path -- it's a
host, followed by a path, which together form a scheme-relative URL.
I'm not quite convinced that value is actually the right thing in
2 of the 3 places we use it, but fixing that can start by giving an
accurate name to the thing we have.
Greg Price
Abhijeet Kaur