Add replaceable values support

[stan-spotts]

Not sure if anyone is actively watching and willing to make changes, but... given that one will be testing these policies in a dev, qa, etc., environment prior to deploying to production, it would be useful to support having replaceable values in the action. A set of key=value pairs, maybe allow the specification of the "quotes" that surround the keys to replace?

[CodingBlob]

I use the VSCode plugin which enables me to add variables to the policy files. Would be great to have support for gh actions to replace the values during build so we dont have to build it locally on the computer.
https://marketplace.visualstudio.com/items?itemName=AzureADB2CTools.aadb2c