User-installed Grafana plugins unaffected by PMM upgrade

STR:

1. Install PMM 2.4.0
2. Execute on PMM server:

    [[email protected] opt]# grafana-cli plugins install alexanderzobnin-zabbix-app
   installing alexanderzobnin-zabbix-app @ 3.11.0
   from: https://grafana.com/api/plugins/alexanderzobnin-zabbix-app/versions/3.11.0/download
   into: /var/lib/grafana/plugins
   
   ✔ Installed alexanderzobnin-zabbix-app successfully 
   
   Restart grafana after installing plugins . <service grafana-server restart>
   
   [[email protected] opt]# ls 
   ansible  entrypoint.sh
   [[email protected] opt]# ls -la /var/lib/grafana/plugins/
   total 48
   drwxr-xr-x 1 root    root    4096 Apr  8 20:54 .
   drwxr-xr-x 1 grafana grafana 4096 Mar 18 12:54 ..
   drwxr-xr-x 5 root    root    4096 Mar 18 12:54 NatelEnergy-grafana-discrete-panel-f2c7e64
   drwxr-xr-x 5 root    root    4096 Mar 18 12:54 Vertamedia-clickhouse-grafana-995b21b
   drwxr-xr-x 8 root    root    4096 Apr  8 20:54 alexanderzobnin-zabbix-app
   drwxr-xr-x 5 root    root    4096 Mar 18 12:54 digiapulssi-grafana-breadcrumb-panel-42481fe
   drwxr-xr-x 6 root    root    4096 Mar 18 12:54 grafana-grafana-polystat-panel-a1347fb
   drwxr-xr-x 6 root    root    4096 Mar 18 12:54 grafana-piechart-panel-ec46c48
   drwxr-xr-x 5 root    root    4096 Mar 18 12:54 jdbranham-grafana-diagram-bcecc9d
   drwxr-xr-x 5 root    root    4096 Mar 18 12:54 petrslavotinek-grafana-carpetplot-81535f2
   drwxr-xr-x 3 root    root    4096 Mar 18 12:53 pmm-app
   drwxr-xr-x 7 root    root    4096 Mar 18 12:54 yesoreyeram-yesoreyeram-boomtable-panel-3c1ad62

3. Upgrade to PMM 2.5.0
4. Check Grafana plugins dir:
   *Given result: *

    [[email protected] opt]# ls -la /var/lib/grafana/plugins/ 
   total 44
   drwxr-xr-x 11 root    root    4096 Apr  8 20:59 .
   drwxr-xr-x  1 grafana grafana 4096 Apr  8 20:59 ..
   drwxr-xr-x  5 root    root    4096 Apr  8 20:59 digiapulssi-breadcrumb-panel
   drwxr-xr-x  4 root    root    4096 Apr  8 20:59 grafana-piechart-panel
   drwxr-xr-x  5 root    root    4096 Apr  8 20:59 grafana-polystat-panel
   drwxr-xr-x  5 root    root    4096 Apr  8 20:59 jdbranham-diagram-panel
   drwxr-xr-x  5 root    root    4096 Apr  8 20:59 natel-discrete-panel
   drwxr-xr-x  5 root    root    4096 Apr  8 20:59 petrslavotinek-carpetplot-panel
   drwxr-xr-x  3 root    root    4096 Apr  8 19:39 pmm-app
   drwxr-xr-x  5 root    root    4096 Apr  8 20:59 vertamedia-clickhouse-datasource
   drwxr-xr-x  7 root    root    4096 Apr  8 20:59 yesoreyeram-boomtable-panel

Expected result: Installed plugins are not removed