Expand Snaps Insights API to support the confirmations alert system

[FrederikBolding]

Need defining further and a SIP to be written.

For now we probably want to treat critical severity as a flag to add to the alerts system instead of the modal we've previously used: https://github.com/MetaMask/metamask-extension/blob/develop/ui/pages/confirmations/hooks/useConfirmationAlerts.ts#L60

The problem is that the alert system currently doesn't support any UI besides text. We'll need to resolve that before proceeding.