ARO-13789 Add support for deleting LB probes

[dmichellis]

Which issue this PR addresses:

https://issues.redhat.com/browse/ARO-13789

Adds deletion for LB probes

What this PR does / why we need it:

This addresses an issue that happened during an incident (TODO: more info pending) where upgrades were stuck, and some restarts were required to complete the upgrade. Resources were left orphaned and couldn't be deleted.

Test plan for issue:

There are unit tests for both API calls and the loadbalancer logic in the RP

Is there any documentation that needs to be updated for this PR?

TODO: organise the information about the incident

How do you know this will function as expected in production?

Adding new special-case resource deletion, like FrontendIP, that only exists as references in the loadbalancer configuration.

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[ehvs]

Deleting line 96 should fix the error.
Running make lint-go may help test locally to brush off before PR opening.

[aasserzo]

Maybe add a check for nil/empty vars here?

[kimorris27]

The Azure SDK for Go has a function that will make this easier and safer: https://pkg.go.dev/github.com/Azure/azure-sdk-for-go/sdk/azcore/arm#ParseResourceID

[kimorris27]

I found a bug in the unit tests and made some other small recommendations, but the core functionality LGTM 👍🏻

[kimorris27]

The Azure SDK for Go has a function that will make this easier and safer: https://pkg.go.dev/github.com/Azure/azure-sdk-for-go/sdk/azcore/arm#ParseResourceID

[kimorris27]

Nit: Although it's very unlikely for this to be nil, I think it would be worth checking to avoid panics.

[kimorris27]

We would actually want this to be the original LB - if we try and fail to delete probe 2, both probes should still be left on the load balancer.

The reason the test cases pass as-is is because the originalLB's probes are stored in a pointer, so when we specify currentLB: originalLB in both test cases, the same underlying slice of probes is being used in both test cases. Thus, the first test case removes probe 1, and this change carries over to the second test case. You can validate that this is the case by replacing originalLB with a hard-coded load balancer struct in both test cases - the second test case fails.

I recommend hard-coding the Azure SDK for Go resource structs in each test case to avoid these types of issues. I know it's verbose, but it avoids confusing bugs and makes each test case clearer.