MM-49485: Set BoardsProduct FF to on by default (#22006)

https://mattermost.atlassian.net/browse/MM-49485

```release-note
Boards will be served as an in-built product from
within Mattermost server instead of a plugin.

If you want to disable this, please set the
MM_FEATUREFLAGS_BoardsProduct env var to "false" (without
                                                  the quotes).

In this mode, the boards plugin will remain disabled.
```

model/config.go

@@ -2867,8 +2867,8 @@ func (s *PluginSettings) SetDefaults(ls LogSettings) {
 	}
 
 	if s.PluginStates[PluginIdFocalboard] == nil {
-		// Enable the focalboard plugin by default
-		s.PluginStates[PluginIdFocalboard] = &PluginState{Enable: true}
+		// Disable the focalboard plugin by default
+		s.PluginStates[PluginIdFocalboard] = &PluginState{Enable: false}
 	}
 
 	if s.PluginStates[PluginIdApps] == nil {