DeletePolicy for IBMPowerVSImage

[mkumatag]

/kind feature
/area provider/ibmcloud

Describe the solution you'd like
By default the images associated with the resource from the cloud will get deleted as soon as the resource gets deleted, but in certain environment user may want to retain the images for subsequent runs because every time image import is a costly affair.

Proposing following field to the resource:

// IBMPowerVSImageSpec defines the desired state of IBMPowerVSImage
type IBMPowerVSImageSpec struct {

	// +kubebuilder:default=delete
	// +kubebuilder:validation:Enum=delete;retain
	// +optional
	DeletePolicy string `json:"deletePolicy,omitempty"`
        
}

If policy is set as retain then don't trigger the delete call to the backend

Anything else you would like to add:
[Miscellaneous information that will assist in solving the issue.]

[mkumatag]

/assign @Prajyot-Parab