Be able to specify different local registry to source kube-rbac-proxy

[chris-fewtrell]

Due to the need to comply with internal company security policies its not permitted to directly pull from internet provided registries. Rather it is copied to a local registry and is put through a review/approval process before being made available on that internal/local registry. It would be useful to allow the specification of a registry for the kube-rbac-proxy used in tyk-operator.

Possible Solution

Provide option in yaml to specify a registry to draw the kube-rbac-proxy from, but default to the existing gcr.io/kubebuilder/kube-rbac-proxy if not specified.

Additional Context

Taken from internal Tyk Support ticket 13395

[gernest]

This can be a followup after #360 gets merged since we will be able to customise resources, we can add container image as well.