Use an application-specific private Tracker instance
We should switch to an application-specific private Tracker instance. This means:
We can bundle the Tracker daemons inside the Photos Flatpak and not have to rely on them being provided by the host OS.
The lifetime of the Tracker daemons would be tied to the lifetime of the org.gnome.Photos D-Bus name. This should reduce the impact of various bugs that lead to complaints about Tracker consuming a lot of CPU or I/O resources.
Having an application-specific database means that bugs in other applications won't affect Photos and vice-versa.