Replace k8gb.io/primarygeotag annotation with k8gb.io/primary-geotag

[somaritane]

I know this is minor issue, and there are no strict conventions on k8s annotations.
But primary and geotag in k8gb.io/primarygeotag are two separate words, so it's better to separate them with dash in order to make annotation more readable, avoid authoring errors, and also align with the style used by existing Ingress Controllers known to community (e.g. https://kubernetes.github.io/ingress-nginx/user-guide/nginx-configuration/annotations/, https://doc.traefik.io/traefik/v1.7/configuration/backends/kubernetes/#general-annotations):

--- k8gb.io/primarygeotag
+++ k8gb.io/primary-geotag

[somaritane]

In order to maintain backwards compatibility with existing API, we can add k8gb.io/primary-geotag as alternative and deprecate k8gb.io/primarygeotag later.

[ytsarev]

No issues with the direct switch imho.