Write dynamic configuration

Link out to Terraform expressions and functions. Should include how expressions and functions are similar and different. The main source of this information should come from the following pages:

• https://developer.hashicorp.com/terraform/language/expressions
• https://developer.hashicorp.com/terraform/language/expressions/function-calls
• https://developer.hashicorp.com/terraform/language/functions

Potentially link out to troubleshooting docs too since you may want to experiment with Terraform console and create plan runs before you actually apply the configuration.