[ENHANCEMENT] Instrument the time from request made to staff review

[mrchrisadams]

Is your feature request related to a problem? Please describe.

We currently review every submission coming in, to maintain quality, and we now have a mechanism for flagging providers and datacentres that need to be reviewed so there's a list to run through.

We want an idea of how long it takes to respond to these events with either an approval or request for more information from providers, so we have a useful metric we can measure and optimise over time.

Describe the solution you'd like
A clear and concise description of what you want to happen.

Introducing some notion of a time-span for when data is flagged for review, which ends when a member of staff has reviewed it, and made a decision.

This would ideally be linked to the provider, and track who touched the data between it needing a attention to being resolved.

Describe alternatives you've considered

We already use the django logentry model for instrumenting our app, and we might be able use that if the data exposes the addition and removal of specific tags already.

Otherwise we may need to add some new logic into the models we change themselves.

Additional context
Add any other context or screenshots about the feature request here.