added about azure firewall (bregman-arie#313)

Author: Akbar-Ahmed

certificates/azure-fundamentals-az-900.md

@@ -13,3 +13,13 @@
  * Private - Cloud services having computing resources limited to specific customer or organization, managed by third party or organizations itself
  * Hybrid - Combination of public and private clouds
 </b></details>
+
+
+<details>
+<summary>What is Azure Firewall?</summary><br><b>
+
+Azure Firewall is a cloud-native and intelligent network firewall security service that provides the best of breed threat protection for your cloud workloads running in Azure.
+</b></details>
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+
+