docs: refactor sections, consolidate examples (#1164)

docs/configuration/examples/kubernetes/istio/gateway.yml

@@ -1,41 +0,0 @@
-apiVersion: networking.istio.io/v1alpha3
-kind: Gateway
-metadata:
-  name: internal-gateway
-  namespace: istio-system
-spec:
-  selector:
-    istio: ingressgateway
-  servers:
-  - port:
-      number: 443
-      protocol: HTTPS
-      name: https-default
-    tls:
-      mode: SIMPLE
-      serverCertificate: "sds"
-      privateKey: "sds"
-      credentialName: internal-cert
-    hosts:
-    - *.yourcompany.com
----
-apiVersion: cert-manager.io/v1alpha2
-kind: Certificate
-metadata:
-  name: internal-cert
-  namespace: istio-system
-spec:
-  secretName: internal-cert
-  issuerRef:
-    name: self-signed-issuer
-    kind: ClusterIssuer
-  commonName: *.yourcompany.com
-  dnsNames:
-    - *.yourcompany.com
----
-apiVersion: cert-manager.io/v1alpha2
-kind: ClusterIssuer
-metadata:
-  name: self-signed-issuer
-spec:
-  selfSigned: {}