Draft: Add EteSync provider
Fixes #152
Needs also https://gitlab.gnome.org/zecakeh1/evolution-data-server/-/commit/58450d5379febbdf14de2281eb90f56a4a86f8c7 and https://gitlab.gnome.org/zecakeh1/evolution-etesync/-/commit/14391b6c7c73ee5b5a34f212f5782cbf3f32d163
It relies on evolution-etesync to be installed. Alternatively, we could add a required dependency to libetebase.
Edited by Kévin Commaille