Prompt when the vulnerability database needs updating

[popey]

Similar to #4 - the grype vulnerability database gets published every day. If grype hasn't been executed for more than 12-24 hours, it's likely using an outdated copy. When the user first runs grype manually, by default, it will update the database. This also happens in grummage (when run for the first time, or for the first time in a while) which results in a long delay when opening the first SBOM.

It would be better if, on launch, grummage could detect that grype's vulnerability database is outdated, and tell the user (perhaps in the status bar at the bottom) inform the user. They could perhaps have a key mapped to 'update vuln db' manually.

Alternatively a popup could appear, in which the user is informed 'grype vuln database being updated' while grype db update is run in the background.