fix/indexed-search: add livenessProbe to zoekt-webserver to prevent hung pods

Without a livenessProbe, zoekt-webserver pods that crash silently remain
in an unhealthy state indefinitely. The probe acts as a backup to the
in-process watchdog (failureThreshold=10, period=60s > watchdog's 9x60s
detection window).

ref incident INC-484 https://sourcegraph.slack.com/archives/C0APJUXBG4R

Author: devdinu

charts/sourcegraph/templates/indexed-search/indexed-search.StatefulSet.yaml

@@ -63,6 +63,15 @@ spec:
         ports:
         - name: grpc
           containerPort: 6070
+        livenessProbe:
+          httpGet:
+            path: /healthz
+            port: grpc
+            scheme: HTTP
+          initialDelaySeconds: 120
+          timeoutSeconds: 5
+          periodSeconds: 60
+          failureThreshold: 10
         readinessProbe:
           failureThreshold: 3
           httpGet: