Improve db-backup image

• Add configuration files to the repo (one per host)
• Make the image adapted to CI
• Add a separate docker-compose file
• Use networks rather than links
• Add secrets management

pica-db-backup/config/pica02.json

+{
+  "wekan":
+    {
+      "Host": "wekan-db",
+      "Port": "27017",
+      "Database": "wekan",
+      "Type": "mongo",
+      "Folder": "wekan",
+      "Cron" : "0 */12 * * *",
+      "Init-Backup" : "1",
+      "Backup-Rota":
+          {
+              "Hour" : 24,
+              "Day" : 7,
+              "Week" : 4,
+              "Month" : 12
+          }
+    }
+}