Move Diagnostics types from Management.Abstractions to Management.Endpoint

[bart-vmware]

Description

This PR moves all types in the namespace Steeltoe.Management.Diagnostics in the Steeltoe.Management.Abstractions project to the Steeltoe.Management.Endpoint project.

Comparing changes with Steeltoe 3.x, I found that some types moved from Endpoint to Abstractions in v4. Upon further inspection, it turns out all of these types are exclusively used by the Metrics actuator. In Steeltoe 3.x, they were shared between Core/Base projects, which required them to live in Abstractions.

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[TimHess]

If we still need DiagnosticObserver then I think it (and IDiagnosticObserver) should stay in the Abstractions package for extensibility

[bart-vmware]

Even if we still need them, they remain public and extensible. But it is only used by the metrics actuator, so close to that seems the better place to me.

[TimHess]

Keeping it in Abstractions would be better if (as an example) we wanted to add a DiagnosticObserver for Eureka. Sure it's only used by the endpoint, but another implementation likely wouldn't be in an application and might not want the heavier dependency on Endpoint

[TimHess]

I think there's an argument (though probably undocument) in there somewhere for making IRuntimeDiagnosticSource extensible, so maybe that should stay here

[bart-vmware]

What would that argument be?

[TimHess]

Basically the same as DiagnosticObserver, though I'm a little less confident on this one. Ultimately, we need to get to the bottom of whether we can remove these entirely

This wasn't supposed to be an approval