enable override defaults for redis images

[romanfurst]

Current implementation

since default Redis images are hardcoded, updating redis-operator version might cause all incances of redisdailover cluster are restarted if hardcoded default values has changed. It might be undesirable behavior especially in production environment (assume deploy with gitops argocd)

Propose implementation

default images are externally configurable. You can change redis-operator version but your defined default versions of redisfailover instances stay still -> redisfailover instances not change -> no restart

[SISheogorath]

Personal opinion: I would love to see a Full Qualified Image Name(FQIN, docker.io/library/redis:6.2.6-alpine instead of redis:6.2.6-alpine) since all main kubernetes runtimes (containerd, cri-o, …) allow to override mirroring of registries already, there is no benefit of not using a FQIN.

Some container runtimes can be configured to refuse to start when the image name is not a FQIN, e.g. cri-o with strict configuration. Further it helps to make clear what redis image is actually intended to be used and not just some image that happens to have these tags causing unexpected issues due to different resolution of image names/tags.