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.
```

scripts/test.sh

@@ -14,6 +14,7 @@ COVERMODE=$8
 
 PACKAGES_COMMA=$(echo $PACKAGES | tr ' ' ',')
 export MM_SERVER_PATH=$PWD
+export MM_FEATUREFLAGS_BoardsProduct=false
 
 echo "Packages to test: $PACKAGES"
 echo "GOFLAGS: $GOFLAGS"