Add new Dynamo table for prior lake data

[frankinspace]

PLD = prior lake data

• Reuse existing HydrocronTable class
• create similar module to https://github.com/podaac/hydrocron/blob/develop/hydrocron/db/io/swot_reach_node_shp.py specifically for prior lakes
• update https://github.com/podaac/hydrocron/blob/develop/hydrocron/db/load_data.py to handle prior lake shapefiles
• Should be able to use filename to identify which specific shapefiles contain prior lake data
• Add test cases for loading PLD