gitea: Inherit from Gogs lister
This removes code and adds support for incremental pagination.
While both are essentially the same lister now, it still makes sense to keep the Gitea lister separate, in order to:
- display them in different categories on https://archive.softwareheritage.org/
- support possible divergence of APIs in the future
Migrated from D8289 (view on Phabricator)