Update snapd-glib to 1.48
Changelog:
- New API
- Deprecated API
- Allow searching via common-id
- Add a description markdown parser
- Replace SnapdConnection with SnapdPlugRef and SnapdSlotRef
- Support updated connections API (/v2/connections)
- Support updated /v2/interfaces&select= API
- Support snap configuration API
- Add Qt interface attribute API
- Make snapd_client_set_socket_path revert to the default when NULL passed.
- Fix C99 mode not being enabled on older versions of GCC