Add an example of sql security alert policy (#241)

* add example of sql security alert policy

---------

Co-authored-by: Nanxuan Xu <nanxu@microsoft.com>

quickstart/101-sql-security-alert-policy/variables.tf

@@ -0,0 +1,30 @@
+variable "resource_group_location" {
+  type        = string
+  description = "Location for all resources."
+  default     = "eastus"
+}
+
+variable "resource_group_name_prefix" {
+  type        = string
+  description = "Prefix of the resource group name that's combined with a random ID so name is unique in your Azure subscription."
+  default     = "rg"
+}
+
+variable "sql_db_name" {
+  type        = string
+  description = "The name of the SQL Database."
+  default     = "SampleDB"
+}
+
+variable "admin_username" {
+  type        = string
+  description = "The administrator username of the SQL logical server."
+  default     = "azureadmin"
+}
+
+variable "admin_password" {
+  type        = string
+  description = "The administrator password of the SQL logical server."
+  sensitive   = true
+  default     = null
+}