Test if we are updating custom_metadata in workflows

[renan-souza]

for dictionary fields, like custom_metadata especially,
# test if we are updating or replacing when
# an existing wf already has custom_metadata and we call this method

flowcept/flowcept/commons/daos/document_db_dao.py

Line 293 in bbbeb55

# TODO: for dictionary fields, like custom_metadata especially,