Revert "Remove Grafana charm"

This reverts commit 027439f8b24c98525475e8f90591c70e053b72fe.

Reason for revert: Grafana-k8s requires Juju 3.1 and we are not ready
to change Juju versions at this time

Change-Id: I2f1056da47a9c0afc63fc2f547dbebbf667d11e6
Signed-off-by: Mark Beierl <mark.beierl@canonical.com>
diff --git a/installers/charm/grafana/templates/default_datasources.yaml b/installers/charm/grafana/templates/default_datasources.yaml
new file mode 100644
index 0000000..88e97df
--- /dev/null
+++ b/installers/charm/grafana/templates/default_datasources.yaml
@@ -0,0 +1,34 @@
+# Copyright 2021 Canonical Ltd.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+#
+# For those usages not covered by the Apache License, Version 2.0 please
+# contact: legal@canonical.com
+#
+# To get in touch with the maintainers, please contact:
+# osm-charmers@lists.launchpad.net
+##
+
+---
+datasources:
+  - access: proxy
+    editable: true
+    is_default: true
+    name: osm_prometheus
+    orgId: 1
+    type: prometheus
+    version: 1
+    url: http://$prometheus_host:$prometheus_port
+    basic_auth: $enable_basic_auth
+    $user
+    $password