Resolve trigger configuration from environment variables

Azure Functions provides a way to load trigger configuration values from an environment variable using an app setting binding expression (i.e. %syntax%) KEDA currently requires some values to be read from an environment variable / secret (e.g. connection strings), but other ones it requires literal values (e.g. queue name). It would be nice if there was also syntax to let KEDA know a value should be resolved from the target deployment environment variable.

Use-Case

As an Azure Functions developer who has built a function with a trigger that uses an app setting binding expression, I want to have similar syntax resolved by KEDA to resolve trigger configuration from environment variables, so that I have a consistent experience with trigger configuration (including connection strings) and am not forced to write alternative solutions such as Helm charts.

Specification

• Trigger configuration should optionally be resolved from environment variables
• KEDA should support syntax which allows a developer to indicate trigger configuration is to be resolved from environment variables
• Syntax used to indicate configuration from environment variables should be consistent for all trigger configuration (not specific to connection strings)