support k8s 1.18+ with backward compatibility

[freeznet]

kubectl apply -f cloud.streamnative.io_functions.yaml will cause following error, which will break the CI tests of function mesh java proxy.

The CustomResourceDefinition "functions.cloud.streamnative.io" is invalid: 
* spec.validation.openAPIV3Schema.properties[spec].properties[pod].properties[initContainers].items.properties[ports].items.properties[protocol].default: Required value: this property is in x-kubernetes-list-map-keys, so it must have a default or be a required property
* spec.validation.openAPIV3Schema.properties[spec].properties[pod].properties[sidecars].items.properties[ports].items.properties[protocol].default: Required value: this property is in x-kubernetes-list-map-keys, so it must have a default or be a required property

[freeznet]

As a result of: kubernetes/kubernetes#88076 that is included in k8s 1.18 (https://github.com/kubernetes/kubernetes/blob/master/CHANGELOG/CHANGELOG-1.18.md#other-api-changes) keys have to be either required or have a default value.

[freeznet]

#104 fixes the ci tests issue with align k8s version to 1.15, but the CRD is still not working with 1.18+, will look into it later.

[freeznet]

update the API version to v1

[freeznet]

fixed by #328