fix: use case-insensitive boolean parsing for OCPP configuration values

fix: use case-insensitive boolean parsing for OCPP configuration values

- Replace strict string comparisons (=== 'true'/'false') with
  convertToBoolean() or .toLowerCase() across OCPP 1.6 and 2.0 stacks
- Add missing OCPP 1.6→2.0 key mappings for HeartbeatInterval,
  HeartBeatInterval, and WebSocketPingInterval
- Add missing readonly field to 4 chargex template configuration keys
- Add .trim() to convertToBoolean for whitespace-padded values