loki-ca: Add cert-manager issuer for Loki CA

The Loki CA is used to issue client certificates for Grafana Loki.  This
_cert-manager_ ClusterIssuer will allow applications running in
Kubernetes (e.g. Grafana) to request a Certificate that they can use to
access the Loki HTTP API.

loki-ca/loki-ca.yaml

@@ -0,0 +1,13 @@
+apiVersion: v1
+kind: Namespace
+metadata:
+  name: loki-ca
+
+---
+apiVersion: cert-manager.io/v1
+kind: ClusterIssuer
+metadata:
+  name: loki-ca
+spec:
+  ca:
+    secretName: loki-ca