Add support for legacy database writers (#8)

* Treat default "postgres" user as writer for all databases

* fmt

* more generic approach

Author: tun0

locals.tf

@@ -11,14 +11,21 @@ locals {
       }
     ]
   ])
-  databases_writers = flatten([
+  databases_writers = flatten(concat([
     for role, role_ in var.roles : [
       for database in role_.databases_rw : {
         role     = role
         database = database
       }
     ]
-  ])
+    ], [
+    for database in local.databases : [
+      for writer in var.legacy_writers : {
+        role     = writer
+        database = database
+      }
+    ]
+  ]))
 
   privileges_ro = [
     "SELECT",

variables.tf

@@ -1,3 +1,8 @@
+variable "legacy_writers" {
+  type    = list(string)
+  default = []
+}
+
 variable "roles" {
   type = map(object({
     databases_ro = list(string)