Adding cluster-issuer annotation for TLS provisioning

Through the usage of cert-manager, the charms will be able
request TLS certificates to protect the Kubernetes Ingress
endpoint that is exposed.

Note: Cert-manager must be configured ahead of time.

Change-Id: I7dacdb8dca2f78664c5604e509e2516ae6023d06
Signed-off-by: sousaedu <eduardo.sousa@canonical.com>
diff --git a/installers/charm/mysqld-exporter/config.yaml b/installers/charm/mysqld-exporter/config.yaml
index a3aaa21..8d3703e 100644
--- a/installers/charm/mysqld-exporter/config.yaml
+++ b/installers/charm/mysqld-exporter/config.yaml
@@ -37,3 +37,7 @@
     type: string
     description: Ingress URL
     default: ""
+  cluster_issuer:
+    type: string
+    description: Name of the cluster issuer for TLS certificates
+    default: ""