This slightly modifies the current save code now workflow. Prior to register a new
origin url for "save code now", this first ensures said origin exists (through a HEAD
request done server side).
If the origin does not exist, an explanation notification is provided to the user.
Otherwise, the origin is submitted for registration as usual.
This should decrease the number of visit with not_found status. This also prepares work
for the incoming new bundle visit type (which needs that check).
Related to T3213