[3pt] Synthesize_test_cases metrics CSV has leading zero stripped from HUCs

[CarsonPruitt-NOAA]

I'm thinking it's probably the new option to load in a previous metrics CSV instead of read through the folders isn't treating the HUC column as a string.

inundation-mapping/tools/synthesize_test_cases.py

Lines 277 to 278 in a19ca57

	if prev_metrics_csv is not None:
	prev_metrics_df = pd.read_csv(prev_metrics_csv)

• Add in the option to read in the 'huc' column as str in the line above
• Fix all of the leading zeroes in ALL of the metrics CSVs so they are not propagated to new versions