BuildTokenURLForDomain and BuildTokenURLForSite cannot be merged: a
provider's signed-state Site (e.g. Datadog's region key) is not always the
string its token host needs (the API domain). Spell that out at the switch
so the split is not mistaken for accidental duplication.
Signed-off-by: Aurélien Sibiril <81782+aureliensibiril@users.noreply.github.com>