Change host's health based on software updates discovery result

[nelsonkopliku]

Description

This PR adds the domain logic to handle software updates discovery.

• a new event SoftwareUpdatesDiscoveryCompleted is emitted containing the discovered relevant patches counts. Needed to properly update aggregate state and opens the possibility to project such data if needed and to possibly broadcast via websockets interesting information that might be useful for the UX.
• based on what has been discovered also a HostHealthChanged event might be emitted

I think we might need extra domain interactions related to software updates discovery business process that would allow us to answer the following:

• what happens when a user clears up suma settings? should we invalidate latest discovery data and ignore it in host's aggregated health?
• if we don't do anything when clearing up settings, we might wait for the watch process ™️ next tick, however also in that case we need to decide what to do if a discovery had previously ran, but now we do not have settings anymore.

How was this tested?

Automated tests added.

[dottorblaster]

Just a tiny change request, I think it would simplify the tests as well, let me know what do you think. Great job, keep it up!

[dottorblaster]

[jamie-suse]