Add support for multus cni

[Edward Hope-Morley]

https://ubuntu.com/kubernetes/docs/cni-multus

[Hemanth Nakkina (hemanth-n)]

Not able to deploy multus cni against charmed k8s 1.22

$ juju status
Model Controller Cloud/Region Version SLA Timestamp
my-k8s-model1 hemanth-n my-k8s-cloud1/default 2.9.16 unsupported 10:04:24Z

App Version Status Scale Charm Store Channel Rev OS Address Message
multus res:multus-image@5d44a83 error 1 multus charmstore stable 18 kubernetes creating or updating custom resource definitions: ensuring custom resource definition "network-attachment-definitions.k8s.cni.cncf.io" with version "v1beta1": the server could not find the requested resource

Unit Workload Agent Address Ports Message
multus/0* waiting idle waiting for container

$ kubectl version
Client Version: version.Info{Major:"1", Minor:"22", GitVersion:"v1.22.3", GitCommit:"c92036820499fedefec0f847e2054d824aea6cd1", GitTreeState:"clean", BuildDate:"2021-10-29T02:41:56Z", GoVersion:"go1.16.9", Compiler:"gc", Platform:"linux/amd64"}
Server Version: version.Info{Major:"1", Minor:"22", GitVersion:"v1.22.3", GitCommit:"c92036820499fedefec0f847e2054d824aea6cd1", GitTreeState:"clean", BuildDate:"2021-10-29T02:20:00Z", GoVersion:"go1.16.9", Compiler:"gc", Platform:"linux/amd64"}

CRD NetworkAttachmentDefinition template seems not in sync with schema of CRD apiextensions.k8s.io/v1
https://github.com/charmed-kubernetes/charm-multus/blob/master/src/charm.py#L150-L184

Should follow this
https://kubernetes.io/docs/reference/using-api/deprecation-guide/#customresourcedefinition-v122

Example:
https://kubernetes.io/docs/tasks/extend-kubernetes/custom-resources/custom-resource-definitions/#create-a-customresourcedefinition

Need to take a look further

[Hemanth Nakkina (hemanth-n)]

Submitted a bug and PR for the problem mentioned in #1 in charm-multus

https://bugs.launchpad.net/charm-multus/+bug/1957032