storage: Add manifest for Longhorn

I was originally going to use GlusterFS to provide persistent storage
for pods, but [Heketi][0], the component that provides the API for
the Kubernetes StorageClass, is in "deep maintenance" status and looks
to be practically dead.  I was a bit afraid to try to use it because of
that, and went looking for guidance on Reddit, which is how I discovered
Longhorn.

storage/README.md

@@ -0,0 +1,31 @@
+# Persistent Storage Using Longhorn
+
+[Longhorn] is a Kubernetes-native persistent storage system.  It is quite
+complex, but installing it is fairly straightforward.
+
+[Longhorn]: https://longhorn.io
+
+
+## Installation
+
+This is mostly based on the official [Install with Kubectl][0] instructions.
+I wanted to add node selectors to the user-deployed and system-managed
+components, to ensure that Longhorn only runs on x86_64 nodes, per the
+[Node Selector][1] instructions.
+
+```sh
+kubectl apply -f longhorn.yaml
+```
+
+
+## Ingress
+
+Expose the Longhorn UI outside the cluster:
+
+```sh
+kubectl apply -f longhorn-ingress.yaml
+```
+
+
+[0]: https://longhorn.io/docs/1.3.0/deploy/install/install-with-kubectl/
+[1]: https://longhorn.io/docs/1.3.0/advanced-resources/deploy/node-selector/

storage/longhorn-ingress.yaml

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+apiVersion: networking.k8s.io/v1
+kind: Ingress
+metadata:
+  name: longhorn-ingress
+  namespace: longhorn-system
+  annotations:
+    # type of authentication
+    nginx.ingress.kubernetes.io/auth-type: basic
+    # prevent the controller from redirecting (308) to HTTPS
+    nginx.ingress.kubernetes.io/ssl-redirect: 'false'
+    # name of the secret that contains the user/password definitions
+    nginx.ingress.kubernetes.io/auth-secret: basic-auth
+    # message to display with an appropriate context why the authentication is required
+    nginx.ingress.kubernetes.io/auth-realm: 'Authentication Required '
+    # custom max body size for file uploading like backing image uploading
+    nginx.ingress.kubernetes.io/proxy-body-size: 10000m
+spec:
+  ingressClassName: nginx
+  rules:
+  - host: longhorn.pyrocufflink.blue
+    http:
+      paths:
+      - pathType: Prefix
+        path: /
+        backend:
+          service:
+            name: longhorn-frontend
+            port:
+              number: 80