[Task]: Track the length of time an add-on is in the review queue

[abyrne-moz]

Description

Measure on a per review basis from when an add-on entered the review queue to a decision being made.

Acceptance Criteria

  ### Milestones/checkpoints
  - [ ] As a PM, I'm able to query the length of time an add-on review took, or aggregate them into averages for reporting purposes.

Checks

• [X] If I have identified that the work is specific to a repository, I have removed "repository:addons-server" or "repository:addons-frontend"

┆Issue is synchronized with this Jira Task

[diox]

Once https://github.com/mozilla/addons/issues/15072 is implemented we should be very close to having that already by looking at when the first NeedsHumanReview was created for a version compared to when it was modified: they should only be modified when is_active is flipped, which is when the review is done.

The only reason this doesn't work right now is that we mass-update multiple NHR at once when a review is done, so auto_now doesn't trigger, so modified isn't updated. But we could trivially add it ourselves.

The query would need to take into account the following things:

• A given version can have multiple reasons for being in the queue, not necessarily created at the same time
• Some specific reasons can trigger a version to be re-added to the queue (appeal, developer reply, abuse reports)
• Versions can enter the queue inheriting the due date of a previously waiting version (since on listed channel there is a maximum of one version awaiting review at all times) - the old version is never reviewed, and the new one should wait for a shorter time

[diox]

Also specifically for DSA-related reasons, those are separate, so an add-on can be reviewed while leaving it in the queue because of those reasons