Track the daily number of valid issues

[karlcow]

When an issue is moved from [needstriage | needsdiagnosis] to something which is

• duplicate
• needscontact
• contactready
• sitewait

It is a valid issue.

Or do we want to track the number of issues getting into needsdiagnosis every day?

We could do both.

@denschub

[karlcow]

To take into consideration that the number might need to be retroactively modified.