v5.0.0 GA Cutover

[nscuro]

Umbrella tracking issue for the cutover process of the v5.0.0 GA release.

• Rename v5 apiserver image and add v5 tag policy #6103
• Rename v5 frontend image and add v5 tag policy #6104
• Freeze dependency-track:master ahead of v5 cutover #6105
• Freeze frontend:master ahead of v5 cutover #6106
• Rehearse v5 release pipeline and image tag set #6107
• Cut over apiserver and publish 5.0.0 GA #6108
• Cut over frontend and publish 5.0.0 GA #6109
• Accept dependency-track workflow dispatches in docs #6110
• Pin helm-charts to v5 (RC validation, then GA) #6111
• Deprecate bare :snapshot and flip :latest to v5 at v4 EOL #6112