[Backup Service] 'backup_task_run' stat is not populated

Description:

The 'backup_task_run' stat does not seem to be populated

http://10.112.210.101:8091/pools/default/stats/range/backup_task_run

Steps to reproduce:

1. Create a repository and take a one off or scheduled backup (I took a scheduled backup followed by a one off backup).

2. Fetch the 'backup_task_run' stat and observe the response is not populated.

http://10.112.210.101:8091/pools/default/stats/range/backup_task_run

{"data":[],"errors":[]}

What I expected to happen:

I expected the stat to indicate that two tasks have been dispatched.

Side note

The the backup_dispatched stat is working correctly.

http://10.112.210.101:8091/pools/default/stats/range/backup_dispatched

{"data":[{"metric":{"nodes":["10.112.210.101:8091"],"cluster":"self","instance":"backup","name":"backup_dispatched","repository":"my_repo","result":"success","state":"active"},"values":[[1603580697,"2"],[1603580707,"2"],[1603580717,"2"],[1603580727,"2"],[1603580737,"2"],[1603580747,"2"],[1603580757,"2"]]}],"errors":[]}

The values field tracks the stat. It is list of time since the epoch followed by the stat at that time e.g. [1603580757, "2"] suggests the stat 'backups_dispatched' is 2 at time 1603580757 (I think that's seconds since the epoch).