[Task]: Show "pending" activity in devhub for all versions and not just the latest one

[diox]

Description

In devhub, in the version list page, if there is a reviewer comment or any other activity needing a reply from the developer as the last activity for a version, we show a count of such activities, but only for the latest version in each channel.

Since https://github.com/mozilla/addons/issues/1981, reviewers and developers will be able to leave comments for each other on any version, so we should extend that "pending" count feature to all versions and not just the latest on each channel, allowing the developer to easily see which one needs a reply.

Acceptance Criteria

  ### Milestones/checkpoints
  - [ ] The count of "pending" activities is shown for all versions

Checks

• [X] If the issue is ready to work on, I have removed the "needs:info" label.
• [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]

Easiest way to set up this scenario is to have an add-on with multiple versions in the same channel and then leave a reply on all the versions in reviewer tools.

A fancier variant: set up some versions without replies, some versions with multiple replies, some versions where the developer has replied to the reviewer, and some versions where the same reviewer reply was posted on multiple versions at the same time (https://github.com/mozilla/addons/issues/1981 allows this).

In any case the count should be shown in the version list for the add-on in devhub, and when clicking to view the replies the "unread" reviewer replies (that don't have a developer reply more recent) should be highlighted and match the count.

[ioanarusiczki]

Lgtm. Sending a reply from email would reset the count for a version. Or when it's replied from dev hub.