Remove unnecessary blank imports (round 2) (#23310)

I mistakenly assumed that those packages are naturally imported.

And also atleast one test would have broken.

None of them are true. :)

So we just import it again at a better place

This reverts commit 30a053314b.

```release-note
NONE
```

server/cmd/mattermost/main.go

@@ -14,6 +14,10 @@ import (
 
 	// Enterprise Imports
 	_ "github.com/mattermost/mattermost-server/server/v8/channels/imports"
+
+	// Blank imports for each product to register themselves
+	_ "github.com/mattermost/mattermost-server/server/v8/boards/product"
+	_ "github.com/mattermost/mattermost-server/server/v8/playbooks/product"
 )
 
 func main() {