Support debug configuration for 2.10+ version

https://apisix.apache.org/docs/apisix/next/debug-mode/

Debug mode configuration has changed from the enable_debug config.yaml option into its own debug.yaml file. The current Helm chart does not support this at the moment.

Modify Helm chart to create configmap for debug.yaml and inject into gateway.

conf/debug.yaml
```yaml
basic:
enable: true
```

Start with the APISIX debug-mode documentation and the Helm chart templates that generate the gateway configuration. Use conf/debug.yaml as the expected content, then verify that the chart creates a ConfigMap and makes it available to the gateway.

Written by the indexing model from the issue text.