New function to read Power Platform env vars

[MikeStall]

See here: https://learn.microsoft.com/en-us/power-apps/maker/data-platform/environmentvariables

Key things there:

1. Env vars have both display and logical name.
2. Env vars vars have many types (like json):

Data Type. Select from Decimal number, Text, JSON, Two options, Data source, or Secret.

Given those requirements, looking at something like introducing each variable as a strongly typed constant like this:

Environment.Variable.VarName

• VarName is the display name
• it's scoped to the Variable object in the Environment namespace. The extra "Variable" layer helps avoid conflicts with other names on Environment.