Allow using variables at deploy and setting default values within templates

When setting default values for runtime properties (that can be changed by the launcher), it can be useful to set the default value directly when using the property, when it's not necessary to make the templates handle it in their default values (especially when the change needs to be backported on a maintenance branch).

Needed by NXP-11423, where the property needs to be set very early when deploying the application, and where default values should not need to be handled by runtime modules.