Update gcr.io/kasten-images/frontend Docker tag to v7

This MR contains the following updates:

Package	Type	Update	Change
gcr.io/kasten-images/frontend		major	6.5.14 -> 7.0.0
gcr.io/kasten-images/frontend	ironbank-docker	major	6.5.14 -> 7.0.0
gcr.io/kasten-images/frontend	stage	major	6.5.14 -> 7.0.0

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