Software updates event handler

[nelsonkopliku]

Description

This PR introduces a SoftwareUpdatesDiscoveryEventHandler reacting to SoftwareUpdatesDiscoveryRequested events, getting information from SUMA and dispatching back in the system a CompleteSoftwareUpdatesDiscovery possibly resulting in a host's health change.

What's next:

• make the discovery tick dispatch DiscoverSoftwareUpdates command so that SoftwareUpdatesDiscoveryRequested + event listener is triggered (currently we'd only have a completion event without an initiation event)
• trigger software updates discovery process for all the registered hosts when saving/changing suma settings
• improve consistency between health in hosts list and what gets returned in GET /hosts/:id/software_updates

How was this tested?

Automated tests.

[arbulu89]

Good job!
I dropped some cosmetic related comments mostly.

PD: I commented on the option of handling some errors in the discovery. It is true that it would just be boilerplate code.
I was just wondering how we will notify the user when a discovery fails, because until now, we just print some messages in the logs.

I guess this discussion goes beyond of this PR. Would it make sense to have a discussion about it?

[arbulu89]

i find this always :ok return not really safe or robust.
I would personally check what the discovery returns, and based on that return some error.

We can implement the error function later on, even if it does a simple :skip.
This would give the look that we are dealing with the error (even though initially is doing nothing).

Maybe in the future, we could have some retry strategy, or broadcast some message to the frontend, or anything like that.

I find it a elegant solution at least.

PD: The error function

[arbulu89]

Anyway, as we are not going to do anything with the failure by now, I'm okey to leaving as it is.
Maybe just putting a comment like The error is not being handled, as there is not any strategy for it

[nelsonkopliku]

I agree, some more robust error handling might be beneficial.
I just wanted to get the flow and iterate on errors as per the needs