Draft: Resolve "Update the BigBang HelmRelease with optional `verify` block"

Package Merge Request

Package Changes

Now that we are OCI Helm Charts are signed in registry1, this changes the Flux install of BigBang from a GitRepository to a HelmRepository using cosign verify.

Package MR

N/A

For Issue

Closes #1778 (closed)

Upgrade Notices

(Include any relevant notes about upgrades here or write "N/A" if there are none)

Closes #1778 (closed)