MAINT: Add caosdb config file

.docker/caosdb_client.json

+{
+  "connections": {
+    "default": "julialib-unittest",
+    "julialib-unittest": {
+      "host": "caosdb-server",
+      "port": 8443,
+      "server_certificate_path": "/cert/caosdb.cert.pem",
+      "authentication": {
+        "type": "plain",
+        "username": "admin",
+        "password": "caosdb"
+      }
+    },
+    "local-caosdb": {
+      "host": "localhost",
+      "port": 8443,
+      "server_certificate_path": "some/path/cacert.pem",
+      "authentication": {
+        "type": "plain",
+        "username": "me",
+        "password": "secret!"
+      }
+    }
+  },
+  "extension": {
+    "this is my": "special option"
+  }
+}