fix: Revert removal of templates provider (#883)

Broke use case of passing in custom template content. Reverts most of the following PRs:
- #865
- #863 
- #854

versions.tf

@@ -5,6 +5,7 @@ terraform {
     aws        = ">= 2.52.0"
     local      = ">= 1.4"
     null       = ">= 2.1"
+    template   = ">= 2.1"
     random     = ">= 2.1"
     kubernetes = ">= 1.11.1"
   }