🐛 Add soft ownership from clusters to ClusterResourceSetBinding

[fabriziopandini]

What this PR does / why we need it:
#7680 removed the owner reference from cluster to ClusterResourceSetBinding, replacing it with a spec.ClusterName field

However, we did not fix the fake objects used for validating clusterctl move accordingly, and thus even if unit tests for move were passing, we are seeking flakiness in CI because there is no more a deterministic order between Cluster and ClusterResourceSetBinding (see details in the attached issue).

This PR fixes this issue by introducing soft ownership from clusters to ClusterResourceSetBinding; It also fixes the softOwnership test that was not really up to date with what the function is currently doing.

Which issue(s) this PR fixes:
Fixes #8316

[fabriziopandini]

/test pull-cluster-api-e2e-full-main

[fabriziopandini]

/test pull-cluster-api-e2e-informing-main
this error seems unrelated

[fabriziopandini]

first run passed, trying to see if it works consistently
/test pull-cluster-api-e2e-full-main

[sbueringer]

/assign @ykakarap

[fabriziopandini]

also second run passed, trying one more
/test pull-cluster-api-e2e-full-main

[fabriziopandini]

3 over 3 success, last one
/test pull-cluster-api-e2e-full-main

[ykakarap]

/lgtm

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: e1804cf848676075c58163bf5157d921ef3f4e9d

[sbueringer]

/lgtm
/approve

Thx for the quick fix!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: sbueringer

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[sbueringer]

/cherry-pick release-1.4

[k8s-infra-cherrypick-robot]

@sbueringer: once the present PR merges, I will cherry-pick it on top of release-1.4 in a new PR and assign it to you.

In response to this:

/cherry-pick release-1.4

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[k8s-infra-cherrypick-robot]

@sbueringer: new pull request created: #8323

In response to this:

/cherry-pick release-1.4

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[johannesfrey]

/area clusterctl