feat(diag): use the esp-idf-diag module as a backend

Replace the original diag implementation in idf.py with the new one in a
separate esp-idf-diag python package. The interface is kept the same as
it was. The simple idf.py diag test is also preserved.

Signed-off-by: Frantisek Hrbata <[email protected]>

Author: fhrbata