Related to #4309
Fix the 'sql: Scan error on column index 5, name "usedPercent": converting NULL to float64 is unsupported' error on the metrics page.
* Update the `getMemoryMetrics` method in `app/Models/Server.php` to handle NULL values for the "usedPercent" field by setting them to 0.0.
* Add a check for NULL values in the `getMemoryMetrics` method before converting to float64.