Added script to update agent version

Source/Public/Update-VSTeamAgent.ps1

@@ -0,0 +1,22 @@
+function Update-VSTeamAgent {
+   param(
+      [Parameter(Mandatory = $true, ValueFromPipeline = $true, Position = 0)]
+      [int] $PoolId,
+
+      [parameter(Mandatory = $true, ValueFromPipeline = $true, ValueFromPipelineByPropertyName = $true, Position = 1)]
+      [Alias('AgentID')]
+      [int[]] $Id
+   )
+
+   process {
+      foreach ($item in $Id) {
+         try {
+            _callAPI -Method Post -Area "distributedtask/pools/$PoolId" -Resource messages -QueryString @{agentId=$item} -Version $([VSTeamVersions]::DistributedTask) -ContentType "application/json" | Out-Null
+            Write-Output "Update agent $item"
+         }
+         catch {
+            _handleException $_
+         }
+      }
+   }
+}