router-secrets: set named certificates to empty array instead of nil when none found

[stlaz]

This fixed a small-ish bug in the router-secrets observer:

when running the repository-local e2e test, one could observe the following:

E0605 10:01:58.163141       1 base_controller.go:180] "ConfigObserver" controller failed to sync "key", err: .servingInfo.namedCertificates accessor error: <nil> is of the type <nil>, expected []interface{}
I0605 10:01:58.164534       1 event.go:278] Event(v1.ObjectReference{Kind:"Deployment", Namespace:"openshift-authentication-operator", Name:"authentication-operator", UID:"b7da59af-4c37-4be6-b870-c4810f2cd833", APIVersion:"apps/v1", ResourceVersion:"", FieldPath:""}): type: 'Normal' reason: 'ObservedConfigChanged' Writing updated observed config:   map[string]interface{}{
        "oauthServer": map[string]interface{}{
                "corsAllowedOrigins": []interface{}{string(`//127\.0\.0\.1(:|$)`), string("//localhost(:|$)")},
                "oauthConfig":        map[string]interface{}{"assetPublicURL": string("https://console-openshift-console.apps.sl-bn.group-b.devcluster.openshift.com"), "loginURL": string("https://api.sl-bn.group-b.devcluster.openshift.com:6443")},
                "servingInfo": map[string]interface{}{
                        "cipherSuites":      []interface{}{string("TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256"), string("TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256"), string("TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384"), string("TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384"), string("TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305"), string("TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305")},
                        "minTLSVersion":     string("VersionTLS12"),
-                       "namedCertificates": nil,
+                       "namedCertificates": []interface{}(nil),
                },
        },
  }

[stlaz]

/cc @marun @vareti

[stlaz]

/retest

[marun]

/lgtm

[openshift-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: marun, stlaz

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[marun]

/cherry-pick release-4.5

[openshift-cherrypick-robot]

@marun: new pull request created: #342

In response to this:

/cherry-pick release-4.5

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