feat: include template variables in dynamic parameter rendering (#18819)

Closes https://github.com/coder/coder/issues/18671

Template variables now loaded into dynamic parameters.

provisioner/terraform/parse.go

@@ -15,6 +15,10 @@ import (
 )
 
 // Parse extracts Terraform variables from source-code.
+// TODO: This Parse is incomplete. It uses tfparse instead of terraform.
+// The inputs are incomplete, as values such as the user context, parameters,
+// etc are all important to the parsing process. This should be replaced with
+// preview and have all inputs.
 func (s *server) Parse(sess *provisionersdk.Session, _ *proto.ParseRequest, _ <-chan struct{}) *proto.ParseComplete {
 	ctx := sess.Context()
 	_, span := s.startTrace(ctx, tracing.FuncName())