Fix concurrent error in cosmosdb example (#191)

* fix concurrent error in cosmosdb example

* change to random_string to reduce the collision rate

* fix 101-cosmos-db-free-tier account name too long issue

---------

Co-authored-by: zjhe <hezijie@microsoft.com>

quickstart/101-cosmos-db-free-tier/main.tf

@@ -4,7 +4,7 @@ resource "azurerm_resource_group" "example" {
 }
 
 resource "azurerm_cosmosdb_account" "example" {
-  name                      = "${random_pet.prefix.id}-cosmosdb-account"
+  name                      = random_pet.prefix.id
   location                  = var.cosmosdb_account_location
   resource_group_name       = azurerm_resource_group.example.name
   offer_type                = "Standard"