Estimation: try to set default values to ease estimation

[xlr-8]

In case where the HCL are modules, it might happen that not all variables are specified. It would be interesting to see if we can set those variables with some default values to highlight how much it got estimated by default. So instance type, counts, etc could be defaulted to certain value.

I'm not sure how do-able that is, but still seems interesting to take a look as Terraform knows both the name, type and potential values associated with it.