Make fact object updatable in database

[zugao]

Summary

• Make fact object updatable as it is already for products.

Checklist

• Categorize the PR by setting a good title and adding one of the labels:
  bug, enhancement, documentation, change, breaking, dependency
  as they show up in the changelog

[glrf]

LGTM

I could nitpick a little and make a propose that we use INSERT .. ON CONFLICT UPDATE .. and simplify all this, but it's fine as is and the products already work the same way :)

[zugao]

I could nitpick a little and make a propose that we use INSERT .. ON CONFLICT UPDATE .. and simplify all this, but it's fine as is and the products already work the same way :)

We plan to do major refactoring of exoscale-metrics-collector and cloudscale-metrics-collector by merging them. I would add your valuable suggestions there and make sure they are implemented.