Live test should support settings env variables based on output from post deployment script

Currently live test deployment script runs deployment using service specific template file which gets deployed using resource manager service. Environment variables are set based on the output variables mentioned in test-resources.yaml file. This works fine in most cases when resource manager deployment supports all types or permissions and resources.

But in few cases , for e.g. storage service supports new set of permissions for SAS URL and these permissions are currently not supported by SRP to generate a SAS using template based deployment. SAS with these new permissions can only be created using pwsh script.

Current live test resource deployment framework does support running post deployment pwsh script. But issue is that it doesn't provide any mechanism to override or set additional env variables based on this script execution in post deployment step.

We should add support to set env variables if post deployment script returns any such output. Current work around I have added in storage resources for JS is to add ENV variables within post deployment itself but It will be a good idea to support this at one common place.