[Etherpad] Update secrets template

pica-etherpad/secrets/etherpad-app.secrets.example

 ETHERPAD_ADMIN_PASSWORD=password
-ETHERPAD_DB_NAME=database
-ETHERPAD_DB_USER=user
+ETHERPAD_DB_NAME=etherpad-lite
+ETHERPAD_DB_USER=etherpad
 ETHERPAD_DB_PASSWORD=password

pica-etherpad/secrets/etherpad-db.secrets.example

 MYSQL_ROOT_PASSWORD=password
-MYSQL_USER=user
+MYSQL_USER=etherpad
 MYSQL_PASSWORD=password
-MYSQL_DATABASE=database
\ No newline at end of file
+MYSQL_DATABASE=etherpad-lite