Detect applications where app desc is required, but not supplied

[MabezDev]

The IDF bootloader output is kinda scary and unclear as to how to resolve the issue (without looking at idf docs).

espflash knows what format (i.e idf format) the binary is, plus it has the elf file, so we can do this check for the user and politely warn them that this is going to fail, and how to resolve it.