chore(main): release 0.21.0

[github-actions[bot]]

:robot: I have created a release beep boop

0.21.0 (2024-06-28)

Miscellaneous Chores

• release 0.21.0 (7906dfa)

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[github-actions[bot]]

:robot: Release is at https://github.com/vexxhost/magnum-cluster-api/releases/tag/v0.21.0 :sunflower: