feat(apps/prod): add git-cdn instance (#821)

We can use it in CI/CD flows:

```bash
git config --global url."http://git-cdn.apps.svc:8080/".insteadOf https://github.com/

git clone https://github.com/pingcap/tidb.git

```

Signed-off-by: wuhuizuo <wuhuizuo@126.com>

apps/prod/cloudevents-server/release.yaml

@@ -2,10 +2,8 @@ apiVersion: helm.toolkit.fluxcd.io/v2beta1
 kind: HelmRelease
 metadata:
   name: cloudevents-server
-  namespace: flux-system
 spec:
   releaseName: cloudevents-server
-  targetNamespace: apps
   chart:
     spec:
       chart: cloudevents-server

apps/prod/git-cdn/kustomization.yaml

@@ -0,0 +1,5 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+namespace: apps
+resources:
+  - release.yaml

apps/prod/git-cdn/release.yaml

@@ -0,0 +1,48 @@
+apiVersion: helm.toolkit.fluxcd.io/v2beta1
+kind: HelmRelease
+metadata:
+  name: git-cdn
+spec:
+  releaseName: git-cdn
+  chart:
+    spec:
+      chart: git-cdn
+      version: 0.1.0
+      sourceRef:
+        kind: HelmRepository
+        name: ee-ops
+        namespace: flux-system
+  interval: 5m
+  timeout: 5m
+  install:
+    remediation:
+      retries: 3
+  rollback:
+    cleanupOnFail: true
+    recreate: true
+  upgrade:
+    cleanupOnFail: true
+    remediation:
+      retries: 3
+  test:
+    enable: true
+    ignoreFailures: false
+  values:
+    replicaCount: 1
+    resources:
+      limits:
+        cpu: "4"
+        memory: 4Gi
+    nodeSelector:
+      kubernetes.io/arch: amd64
+    volumeMounts:
+      - name: data
+        mountPath: /data
+    volumes:
+      - name: data
+        emptyDir: {}
+    configuration:
+      GITSERVER_UPSTREAM: https://github.com/
+      PACK_CACHE_SIZE_GB: 20
+      # directory where to put cache files
+      WORKING_DIRECTORY: /data

apps/prod/kustomization.yaml

@@ -17,3 +17,4 @@ resources:
   - jenkins-beta
   - cloudevents-server
   - boskos
+  - git-cdn