Enable configuring target variants (espressif#7019)

This change enables picking the right board configuration from the
variants/ folder. Previously, we would always pick the default
configuration (e.g., "esp32" instead of "heltec_wifi_lora_32_V2").

Fix partition names in board.txt (espressif#7120)

* typo edit: 8M flash (FAT to SPIFFS) + FAT to FATFS

* more precize fatfs size in 16M flash partition

* Revert size in 8M with spiffs partition

Added NVS test sketch + test script (espressif#6885)

* Added NVS test sketch + test script

* Added cfg.json with multiple fqbns

* cfg.json missing commas fix

* Changed OPI PSRAM to QSPI accordind to new HW setup.

* disabled PSRAM for ESP32S3

* Reverting PSRAM changes

* Remove Octal flash test

Octal flash needs to be tested locally before each release.