Clean slate: 1h block sizes, remove backfill artifacts

- Changed all namespace block sizes to 1h (was 2h/12h/24h in manifests,
  30d+ in the live cluster due to backfill-era bufferPast hacks)
- Deleted entire backfill/ directory (scripts, pods, runbooks)
- Removed stale 05-m3coordinator.yaml (had backfill namespaces)
- Added 05-m3coordinator-deployment.yaml to kustomization
- Fixed init job health check (/health instead of /api/v1/services/m3db/health)
- Updated .env.example (removed Mimir credentials)
- Added 'Why Backfill Doesn't Work' section to README

05-m3coordinator-deployment.yaml

@@ -0,0 +1,63 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: m3coordinator
+  namespace: m3db
+  labels:
+    app.kubernetes.io/name: m3coordinator
+spec:
+  replicas: 2
+  selector:
+    matchLabels:
+      app.kubernetes.io/name: m3coordinator
+  template:
+    metadata:
+      labels:
+        app.kubernetes.io/name: m3coordinator
+    spec:
+      containers:
+        - name: m3coordinator
+          image: quay.io/m3db/m3coordinator:v1.5.0
+          args:
+            - -f
+            - /etc/m3coordinator/m3coordinator.yml
+          ports:
+            - name: api
+              containerPort: 7201
+            - name: metrics
+              containerPort: 7203
+          livenessProbe:
+            httpGet:
+              path: /health
+              port: 7201
+            initialDelaySeconds: 30
+            periodSeconds: 10
+          readinessProbe:
+            httpGet:
+              path: /health
+              port: 7201
+            initialDelaySeconds: 5
+            periodSeconds: 5
+          volumeMounts:
+            - name: config
+              mountPath: /etc/m3coordinator
+      volumes:
+        - name: config
+          configMap:
+            name: m3coordinator-config
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: m3coordinator
+  namespace: m3db
+spec:
+  selector:
+    app.kubernetes.io/name: m3coordinator
+  ports:
+    - name: api
+      port: 7201
+      targetPort: api
+    - name: metrics
+      port: 7203
+      targetPort: metrics