While there is a product entry for Grantlee, I'd think we would simply add a new, given KTextTemplate is to some degree a fork and might have issues of its own, also will it make finding the product easier.
To match the pattern of existing entries for KF modules, I'd think the name should be
frameworks-ktexttemplate
Compare also https://bugs.kde.org/describecomponents.cgi
Description would be copied from https://invent.kde.org/sysadmin/repo-metadata/-/blob/master/projects-invent/libraries/ktexttemplate/metadata.yaml#L1:
Library to allow application developers to separate the structure of documents from the data they contain.
Any proposals who should be default assginee? kxmlgui has kdelibs bugs, for some community-like email address. Perhaps there should be some kf-bugs instead, to match the KF product name?