Expose a resources field in the MariaDB launch form (Onyxia schema)

## Summary

The **mariadb** chart's Onyxia values schema doesn't expose a `resources` field in the launch form. As a result, users can't set CPU/memory requests and limits when starting a MariaDB service, and the chart deploys with no resources on its containers.

This breaks deployment on any namespace enforcing a `ResourceQuota` that requires `limits.cpu`/`limits.memory`: the pod is rejected with `must specify limits.cpu/limits.memory`. The **postgresql** chart from this same repo exposes resources and works fine on the same namespace.

## Request

Add a `resources` section to the mariadb chart's Onyxia schema (`values.schema.json`), mapped onto `primary.resources`, with requests/limits sliders for CPU and memory — same as the `resources.json` schema used in `helm-charts-interactive-services`, and consistent with what postgresql already does.

Sensible defaults so the service works out of the box on quota-enforced clusters would be appreciated (e.g. requests `300m` / `512Mi`, limits `2` / `2Gi`).