improve configurability and resource references for internal ALB (#3654)

* refactor(net-lb-app-ext): improve configurability and resource references

- Allow overriding names for backend buckets and instance groups
- Add optional per-group description with default value
- Use self_link for instance group backend references
- Fix HTTP proxy name to use http_proxy_config

* reverted the instance group reference in backend service back to id instead of self link

* updated all the lb modules for unmanaged instance groups to have flexible names and proper refactorization of http_proxy_cofig in each module

* removed the description variable

* updated the readme.md for the net-lb-app-ext-regional module

* fixed the linting error for the change in versions.tf

---------

Co-authored-by: Julio Castillo <jccb@google.com>
Co-authored-by: Ludovico Magnocavallo <ludomagno@google.com>

modules/net-lb-ext/groups.tf

@@ -20,8 +20,8 @@ resource "google_compute_instance_group" "default" {
   for_each    = var.group_configs
   project     = var.project_id
   zone        = each.value.zone
-  name        = "${var.name}-${each.key}"
-  description = var.description
+  name        = coalesce(each.value.name, "${var.name}-${each.key}")
+  description = each.value.description
   instances   = each.value.instances
 
   dynamic "named_port" {