* Fetch USER env var once
Fetch the USER env var once instead of multiple times for faster DevConfig func execution time
* Set Azure unique prefix and USER as optional
Use an Azure unique prefix for the Azure resources that ARO-RP is using instead of always fetching the USER. When AZURE_UNIQUE_PREFIX env var is not set, then use the USER env var
* Modify more USER references
Rename AZURE_UNIQUE_PREFIX to AZURE_PREFIX, and export the usage of this env var for Azure prefix name resources when it is set. When it is missing use the default USER env var, as before