feat(esp32): added option to add partition before app_0

[daadu]

Some use-case for having partition before app_0:

• storing factory data at fixed offset irrespective of flash size

[daadu]

Any update on this? should be renamed to ESP_IDF_EXTRA_PARTITION_BEFORE_APP ??

[rojer]

storing factory data at fixed offset irrespective of flash size

ok, i understand the need. but there's still one problem here: the NVS size. if it ever needs to be changed, for whatever reason, it's a problem.
so, let's move it to the very top, even before nvs and OTA state, and call the variable something else... ESP_IDF_EXTRA_PARTITION_TOP, perhaps, but if you have a better name - feel free.

[daadu]

If we move this "extra part" at top - then if some one wants to configure it, he has to shift all three default offsets - NVS_ADDR, OTA_DATA_ADDR and APP_OFFSET. In current case only have to shift APP_OFFSET.

Maybe can keep this as well as add "TOP" one?

[daadu]

Or do you think this "shifting" should be handled by MGOS? That is a bit non-trivial - as have make sure that the offset is "aligned" as per ESP spec.