configure command help while building LOOL indicates `loleaflet/dist/branding` as template for branding LOOL but the directory is not present in master. I saw #123893 in which is indicated that those are Collabora-specific files but I can't find those even in Collabora branches.
As discussed on the IRC, the real target of this issue is to provide a list of variables you can add in the branding.js file to brand LOOL and an example "branding" directory.
vars - brandProductName - brandProductURL - brandProductFAQURL are currently known as variables that can be defined via branding.js
This topic is now documented https://wiki.documentfoundation.org/Development/LibreOffice_Online#Branding