Use the value of regresed_by in crafting the training classes for the RegressionRange model

[suhaibmujahid]

Currently, we use the regressionwindow-wanted keyword and the value of the cf_has_regression_range field to determine whether there is a regression range:

bugbug/bugbug/models/regressionrange.py

Lines 76 to 82 in 798f215

	if "regressionwindow-wanted" in bug_data["keywords"]:
	classes[bug_id] = 0
	elif "cf_has_regression_range" in bug_data:
	if bug_data["cf_has_regression_range"] == "yes":
	classes[bug_id] = 1
	elif bug_data["cf_has_regression_range"] == "no":
	classes[bug_id] = 0

We should also use the value of the regresed_by field. If there is a value in the field, we should consider it as "has regression range".