o que significa {} na seção de contêineres no Kubernetes?

Você pode obter documentação usando kubectlos campos dos recursos do Kubernetes. Por exemplo:

$ kubectl explain pod.spec.containers.resources
KIND:       Pod
VERSION:    v1

FIELD: resources <ResourceRequirements>

DESCRIPTION:
    Compute Resources required by this container. Cannot be updated. More info:
    https://kubernetes.io/docs/concepts/configuration/manage-resources-containers/
    ResourceRequirements describes the compute resource requirements.

FIELDS:
  claims    <[]ResourceClaim>
    Claims lists the names of resources, defined in spec.resourceClaims, that
    are used by this container.

    This is an alpha field and requires enabling the DynamicResourceAllocation
    feature gate.

    This field is immutable. It can only be set for containers.

  limits    <map[string]Quantity>
    Limits describes the maximum amount of compute resources allowed. More info:
    https://kubernetes.io/docs/concepts/configuration/manage-resources-containers/

  requests  <map[string]Quantity>
    Requests describes the minimum amount of compute resources required. If
    Requests is omitted for a container, it defaults to Limits if that is
    explicitly specified, otherwise to an implementation-defined value. Requests
    cannot exceed Limits. More info:
    https://kubernetes.io/docs/concepts/configuration/manage-resources-containers/

Se precisar de mais informações sobre qualquer um dos subcampos, basta anexar esse campo ao comando

$ kubectl explain pod.spec.containers.resources.claims
$ kubectl explain pod.spec.containers.resources.limits
$ kubectl explain pod.spec.containers.resources.requests
...

No seu caso, {}significa que nenhum dos campos está definido.