Add a sleep in-between retries (#18853)

* Add a sleep in-between retries

From the logs in production, we have observed that practically
when a deadlock happens, it always fails even after trying 3 times.

Therefore, allowing it some time to recover before trying again.

https://community-daily.mattermost.com/boards/workspace/zyoahc9uapdn3xdptac6jb69ic/285b80a3-257d-41f6-8cf4-ed80ca9d92e5/495cdb4d-c13a-4992-8eb9-80cfee2819a4?c=bf0e73f6-fd69-4d04-88af-53922672b556

```release-note
NONE
```

* Fix conflict with variable names

```release-note
NONE
```

store/layer_generators/retry_layer.go.tmpl

@@ -8,6 +8,7 @@ package retrylayer
 
 import (
 	"context"
+	timepkg "time"
 
 	"github.com/lib/pq"
 	"github.com/mattermost/mattermost-server/v6/model"
@@ -74,6 +75,7 @@ func (s *{{$.Name}}{{$substoreName}}Store) {{$index}}({{$element.Params | joinPa
                     {{$element.Results | errorVar}} = errors.Wrap({{$element.Results | errorVar}}, "giving up after 3 consecutive repeatable transaction failures")
                     return {{genResultsVars $element.Results false }}
                 }
+                timepkg.Sleep(100 * timepkg.Millisecond)
             }
         {{else}}
             return s.{{$substoreName}}Store.{{$index}}({{$element.Params | joinParams}})