Implement a get_df_and_metadata_from_db function

[matthewcarbone]

In order to proceed with #7 I need a more detailed understanding of the API used to get the "data" and "metadata" to use in the Tiled pipeline. I have created a "dummy" scaffold function called get_df_and_metadata_from_db which I need implemented. @elistavitski can you do this? In the meantime, I will work on the code upstream to hook into this function (which we will treat as the endpoint).

The function should look something like this (started in ff529f3):

def get_df_and_metadata_from_db(...):
    # do stuff
    return PANDAS_DATAFRAME, PYTHON_DICT

[matthewcarbone]

Eli, to add a bit more substance to what I'm saying, I have written another "dummy" function here:

def ingest_from_DataBroker(client, db, pbar=True):
    """Loads in all files matching the provided extension.
    NOTE: this will require some check at some point to ensure unique entries
    from databroker are not rewritten every time this function is called
    Parameters
    ----------
    db
    """

    # !!!PSEUDOCODE!!!!!!!!
    for uid in tqdm(db.uids, disable=not pbar):
        df, metadata = get_df_and_metadata_from_db(db, uid, ...)
        # !!!!!!!!!!!!!!!!!!!!!

        res = _process_df_and_metadata(df, metadata)
        _write_from_res(res, client)

This function should in principle crawl Data Broker and upload every (new) entry into Tiled. Note the line

df, metadata = get_df_and_metadata_from_db(db, uid, ...)

This is your endpoint- i.e. where I need your help.