Any background context you want to provide?

What's this PR do?

Adds water meter types: Potable Indoor, Potable Outdoor, Potable: Mixed Indoor/Outdoor
The default display water unit is kGal (thousand gallons) (US)

Provides unit conversions for the following water units to kGal (thousand gallons) (US)

unit_conversion = {
    "ccf (hundred cubic feet)": 0.748,
    "cf (cubic feet)": 0.00748,
    "cGal (hundred gallons) (US)": 0.1,
    "cGal (hundred gallons) (UK)": 0.12,
    "cm (cubic meters)": 0.264172,
    "Gallons (US)": 0.001,
    "Gallons (UK)": 0.0012,
    "kcf (thousand cubic feet)": 7.48,
    "kcm (thousand cubit meters)": 264.172,
    "kGal (thousand gallons) (US)": 1.00,
    "kGal (thousand gallons) (UK)": 1.2,
    "Liters": 0.000264172,
    "Mcf (million cubic feed)": 7480.52,
    "MGal (million gallons) (UK)": 1000,
    "MGal (million gallons) (US)": 1200,
}

NOTE: This does not include support for the other water types avaliable on Portfolio Manager:

Other: Mixed Indoor/Outdoor, Other Indoor, Other Outdoor, Reclaimed: Mixed Indoor/Outdoor, Reclaimed: Indoor, Reclaimed: Outdoor, Well Water: Mixed Indoor/Outdoor, Well Water: Indoor, Well Water: Outdoor

How should this be manually tested?

Upload a file that contains potable water meter data (see JCC_ESPM_clean.xlsx)
Upload its meter data
Check inventory detail meters for a property wtih water meters
Change water meter unit settings in organization settings > units
Check inventory detail meters, meter readings and header should be updated for the chosen units.