soc: esp32: refactor esp32_net

SOC_ESP32_NET is now SOC_ESP32_APPCPU, following espressif's
naming convention in the same manner as ESP32S3 app cpu.

SOC_ESP32_APPCU is now a subset of SOC_SERIES_ESP32.

This commit also changes the necessary files, samples and tests
for bisect purposes.

Signed-off-by: Lucas Tamborrino <lucas.tamborrino@espressif.com>