KEP-4322: add CRD scope explanation to alternatives considered section

[mikemorris]

• One-line PR description:
  Summarizes context from discussions in SIG-Multicluster meetings and https://docs.google.com/document/d/1E_z3ti-d-modwnhsvR3yBZwX4rRpL26dKkl41YAptRo/edit on why a namespace-scoped CRD is recommended over a cluster-scoped CRD for the ClusterProfile resource.

• Issue link: Cluster Inventory API for multicluster management #4322

• Other comments:
  Thanks to @thockin for putting together these illustrations of the possible models for cluster inventory topology.

[k8s-ci-robot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: mikemorris
Once this PR has been reviewed and has the lgtm label, please assign pmorie for approval. For more information see the Kubernetes Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• keps/sig-multicluster/OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[mikemorris]

/retest

[k8s-ci-robot]

@mikemorris: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-enhancements-verify	faffbf7	link	true	/test pull-enhancements-verify

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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-sigs/prow repository. I understand the commands that are listed here.