Ensure existing assets are still clean when a new virus definition is released

[chrislo]

The current implementation of virus scanning in Whitehall rescans all existing assets when a new virus definition file for ClamAV is released.

Asset manager currently does not do that so if we are going to unify the functionality of the two applications we should consider what to do about this feature.

It is noted that the full re-scan of assets takes around 2 days and uses a lock to ensure the process only runs once at a time. If we do implement this feature in Asset Manager we may decide to do it in a different way to avoid this problem.

[chrisroos]

I've added this to the "Bring Whitehall & Mainstream asset behaviour into line with each other" milestone as I think we'll need to do it to ensure we retain the existing Whitehall functionality.

[floehopper]

Daniel has said that there's no specific requirement for this, although it would be a nice-to-have. He's added it to the tech debt and risk registers and said that it's fine for us to de-scope this work.

However, I think it's still worth keeping the issue in case we get a chance to work on it and/or as a reminder to whoever we handover the project to.