Proteced containers: Add icon with number of container protection rules in project setting UI

As suggested by @annabeldunstone, it would be nice to have an icon showing the number of container protection rules in the project setting UI that was introduced by #Protected containers: Show protection rules in ... (#441345 - closed).

The suggestion was part of an MR review and was extracted as a separate issue.

Proposal

Proposal described by @annabeldunstone in this comment: !146523 (comment 1838085406)

Implementation plan

• Finish open MR: Draft: Protected packages + containers: Add cou... (!148699)