Update pica-etherpad/Dockerfile,...

Update pica-etherpad/Dockerfile, pica-etherpad/secrets/etherpad-app.secrets.test, pica-etherpad/secrets/etherpad-db.secrets.test, pica-etherpad/secrets/etherpad-app.secrets.production, pica-etherpad/secrets/etherpad-db.secrets.production files
Deleted pica-etherpad/secrets/etherpad-app.secrets.example, pica-etherpad/secrets/etherpad-db.secrets.example files