twister: reset ESP32 via RTS/DTR to capture early boot logs

When testing ESP32-based platforms in CI, early boot logs can be missed
if the serial connection isn't reset properly. This patch applies the
standard RTS/DTR toggle sequence to reset the ESP32 after flashing,
ensuring consistent log capture from the very beginning.

The logic is applied conditionally when the runner is "esp32".

Signed-off-by: Sylvio Alves <sylvio.alves@espressif.com>