Description of PR

Details:

• Dynamic Request Handling: The RequestsHandler class has been added to handle and modify resource and scheduling requests at the beginning of the CapacityScheduler#allocate method.
• Configuration-Driven Updates: The behavior of the request handler can be configured dynamically via capacity-scheduler.xml configuration, allowing for updates to be applied without restarting the ResourceManager.
• Scriptable Matching: Requests can be matched and modified based on JavaScript expressions, providing flexibility in defining which requests should be updated and how.
• Support for ResourceRequest to SchedulingRequest Conversion: The handler supports converting ResourceRequest objects to SchedulingRequest objects, enabling more advanced scheduling capabilities.

Usage: To enable and configure the request handler, administrators can set the following properties in capacity-scheduler.xml:
yarn.scheduler.capacity.request-handler.enabled: Enables or disables the request handler.
yarn.scheduler.capacity.request-handler.updates: Specifies the JSON configuration for the request updates.

Configuration example:

<property>
  <name>yarn.scheduler.capacity.request-handler.enabled</name>
  <value>true</value>
</property>
<property>
  <name>yarn.scheduler.capacity.request-handler.updates</name>
  <value>
    {
      "items": [
        {
          "appMatchExpr": "queue == 'default'",
          "requestMatchExpr": "priority > 10",
          "isRRToSR": true,
          "partition": "partitionA",
          "executionType": "GUARANTEED",
          "allocationTags": ["tag1", "tag2"],
          "placementConstraint": "and(in,rack,hbase:notin,node,zk)"
        }
      ]
    }
  </value>
</property>

How was this patch tested?

For code changes:

• Does the title or this PR starts with the corresponding JIRA issue id (e.g. 'HADOOP-17799. Your PR title ...')?
• Object storage: have the integration tests been executed and the endpoint declared according to the connector-specific documentation?
• If adding new dependencies to the code, are these dependencies licensed in a way that is compatible for inclusion under ASF 2.0?
• If applicable, have you updated the LICENSE, LICENSE-binary, NOTICE-binary files?