✨ Add MachinePool Machine support in clusterctl discovery

[Jont828]

What this PR does / why we need it: Allow clusterctl discovery to find MachinePool Machines and associated infraMachines.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #4063

[Jont828]

/assign @fabriziopandini

I've separated the clusterctl changes out from the main MPM PR. I think this change should be pretty straightforward to review. WDYT?

[fabriziopandini]

thanks for this PR!
overall lgtm, only one small improvement from my side + if possible, let's add a test case into Test_Discovery

@ykakarap PTAL

[Jont828]

@ykakarap Any thoughts?

[ykakarap]

The overall approach looks good. Can you please add some unit tests for this under Test_Discovery?

[Jont828]

@ykakarap I've added some tests, will rebase today as well.

[fabriziopandini]

/retest

[fabriziopandini]

@Jont828 it seems that some tests are broken after the changes to the fake objects in this PR

[Jont828]

@fabriziopandini Should be fixed (waiting on test results).

[fabriziopandini]

/lgtm
/approve

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: a529dcee344eab00a2d9b593ab0848e5ce30dd9b

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: fabriziopandini

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