Make the presence server to not abort when 'long-term-enabled' isn't set but no request has been set for fetching users by their phone number.
New logic:
- if 'long-term-enabled' hasn't been set but the requests for the users database are set, then abort.
- if 'long-term-enabled' is explicitly set to 'false', then never abort.
- if 'long-term-enabled' is explicitly set to 'true', abort when the requests for the users database aren't properly set.
That has the advantage to warn by a fatal the old users that use long-term presence but have never set 'long-term-enabled' explicitly, as it was 'true' by default before Flexisip 2.0.0 ; but avoiding new user to set exlicitly 'long-term-enabled' as they have to before this fix.