Add healthcheck to report to zui for errors

[AbdelrahmanElawady]

Description

Add healthcheck task to execute multiple checks (only cache for now) and report to zui for errors. It also set flags that can be checked by Power daemon to stop uptime reports.

Changes

• Add and register zui module on zbus to allow other modules to set some errors in the ui.
• Add healthcheck Task that perform checks on the node to make sure everything is OK.
• Add another part in the ui to display errors with the node state.
• Stop uptime reports if cache is unusable (readonly or limited).

Related Issues

• Stop uptime reports for nodes with read only cache disk #2134

Checklist

• Tests included
• Build pass
• Documentation
• Code format and docstring

[AbdelrahmanElawady]

Here is how it looks on the ui:

it was tested using chattr +i /var/cache to make sure creating the file is not possible.

still missing:

• checking the error flag in the uptime goroutine.
• wrapping the errors in zui if the errors are large.
• some docs.

[scottyeager]

This view is a bit confusing, since it shows cache disk: OK above and an error on cache below. I think it's better to write the error in place of the OK message for the cache. If future health checks create the need for a separate errors section, it can be added later.

[AbdelrahmanElawady]

It is showing OK because a check for Readonly cache hasn't been added yet, it will be added with the other remaining changes. A separate section for errors in ZOS node is more helpful to get more details of what is wrong without cluttering the first section (it already has a lot of information) and to support multiple health checks. But that's my opinion.

[scottyeager]

Okay, that makes sense, @AbdelrahmanElawady. In that case it looks good to me.