SpiderMultusConfig: support empty config with custom type

[Icarus9913]

Looking back this issue: #2438
The reason that make the below yaml applied is that the webhook not works by a Webhook configuration mistake that I made, refer to #2067

cat <<EOF | kubectl apply -f -
apiVersion: spiderpool.spidernet.io/v2beta1
kind: SpiderMultusConfig
metadata:
  name: cilium
  namespace: kube-system
EOF

The fix #2438 makes no sense, because we already set the property CniType as a Required field

// MultusCNIConfigSpec defines the desired state of SpiderMultusConfig.
type MultusCNIConfigSpec struct {
	// +kubebuilder:validation:Required
	// +kubebuilder:validation:Enum=macvlan;ipvlan;sriov;ovs;custom
	CniType string `json:"cniType"`

Signed-off-by: Icarus9913 [email protected]

[codecov]

Codecov Report

Merging #2862 (2833db7) into main (fe936b5) will increase coverage by 0.05%.
Report is 2 commits behind head on main.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2862      +/-   ##
==========================================
+ Coverage   81.09%   81.15%   +0.05%     
==========================================
  Files          49       49              
  Lines        5333     5333              
==========================================
+ Hits         4325     4328       +3     
+ Misses        852      850       -2     
+ Partials      156      155       -1     

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unittests	81.15% <ø> (+0.05%)	⬆️

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