fix: remove omitempty from ClientID JSON tag

Remove omitempty from ClientID field in BackendSecurityPolicyAzureCredentials
to maintain consistency with other ID fields and avoid breaking existing
integrations that expect the field to always be present in JSON output.

This addresses the GitHub Copilot review comment in PR #1183.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>
Signed-off-by: Matt Mencel <[email protected]>

Author: MattMencel

api/v1alpha1/backendsecurity_policy.go

@@ -218,7 +218,7 @@ type BackendSecurityPolicyAzureCredentials struct {
 	//
 	// +optional
 	// +kubebuilder:validation:MinLength=1
-	ClientID string `json:"clientID,omitempty"`
+	ClientID string `json:"clientID"`
 
 	// TenantId is a unique identifier for an Azure Active Directory instance.
 	//