fix: Ensure var.region is passed through aws_region data source (#329)

* Use provided region in aws:SourceArn condition

* Remove un-used data source

* Update README

* Restore local.region

Given var.region can be null, add another try() to check for a provided value
before falling back to current region.

* Fix logic

* fix: Correct logic through region data source

---------

Co-authored-by: Bryant Biggs <bryantbiggs@gmail.com>

Author: tvon

modules/service/main.tf

@@ -1,4 +1,6 @@
 data "aws_region" "current" {
+  region = var.region
+
   count = var.create ? 1 : 0
 }
 data "aws_partition" "current" {