This changes the way monitors are initialized to always include
a `manifest` and now they will always log a `start` message.
This makes creation of a monitor symetric accross all monitors
again and no special cases for JSONSeqMonitor are required.
It means one needs to run the json-seq monitor with:
```
$ python3 -m osbuild --monitor=JSONSeqMonitor
```
Fwiw, I'm not 100% confident this is a win but it feels slightly
more right then the special cases in `main_cli.py` that is
replaces.
16c1768780