Added priority queue design pattern (#888)

* added priority queue design pattern

* Minor Refactored, fixed review comments

priority-queue/README.md

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+---
+layout: pattern
+title: Priority Queue Pattern
+folder: priority-queue
+permalink: /patterns/priority-queue/
+categories: Behavioral
+tags:
+ - Java
+ - Difficulty-Beginner
+---
+
+## Intent
+Prioritize requests sent to services so that requests with a higher priority are received and processed more quickly than those of a lower priority. This pattern is useful in applications that offer different service level guarantees to individual clients.
+
+## Explanation
+Applications may delegate specific tasks to other services; for example, to perform background processing or to integrate with other applications or services. In the cloud, a message queue is typically used to delegate tasks to background processing. In many cases the order in which requests are received by a service is not important. However, in some cases it may be necessary to prioritize specific requests. These requests should be processed earlier than others of a lower priority that may have been sent previously by the application.
+
+## Applicability
+Use the Property pattern when
+
+* The system must handle multiple tasks that might have different priorities.
+* Different users or tenants should be served with different priority..
+
+## Real world examples
+
+* [ Priority Queue Pattern](https://docs.microsoft.com/en-us/previous-versions/msp-n-p/dn589794(v=pandp.10))
+Microsoft Azure does not provide a queuing mechanism that natively support automatic prioritization of messages through sorting. However, it does provide Azure Service Bus topics and subscriptions, which support a queuing mechanism that provides message filtering, together with a wide range of flexible capabilities that make it ideal for use in almost all priority queue implementations.