[Python] Add a dummy column that flags ids with consecutive values

I have the following dataframe:

df = pd.DataFrame({"id": ['A', 'A', 'A', 'A', 'B', 'B', 'B', 'B', 'C','C','C','C'],
"date": [2015, 2016, 2017, 2018,
2015, 2016, 2017, 2018,
2015, 2016, 2017, 2018],
"col_1": [1,1,1,0,1,0,1,1,0,1,1,1]})


I want to add a new col that should be a dummy 1 for a group if "col_1" has three consecutive 1s. The resulting data-frame should be:

df_new = pd.DataFrame({"id": ['A', 'A', 'A', 'A', 'B', 'B', 'B', 'B', 'C','C','C','C' ],
"date": [2015, 2016, 2017, 2018,
2015, 2016, 2017, 2018,
2015, 2016, 2017, 2018],
"col_1": [1,1,1,0,1,0,1,1,0,1,1,1],
"col_2": [1,1,1,1,0,0,0,0,1,1,1,1]})

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