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

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

quickstart/101-cosmos-db-serverside-functionality/outputs.tf

@@ -4,4 +4,8 @@ output "cosmosdb_account_id" {
 
 output "cosmosdb_sql_database_id" {
   value = azurerm_cosmosdb_sql_database.main.id
+}
+
+output "cosmosdb_account_name" {
+  value = azurerm_cosmosdb_account.example.name
 }