Support for URI starts with property holder

We should see if we could support smart completion and validation for URI starts with an property placeholder like in the example below.

> ("{{IMPORT_SERVICE_URL}}?ids=$simple{header." + ImportConstants.USER_ID_HEADER + "}&bridgeEndpoint=true"))

We would have to resolve the property placeholder to be able to provide correct syntax for smart completion or validation.

The tricky part is that you could have multiple property files defining the same property. eg "-Dev", "-Test"