Add Experimental Features to change log creation (#8827)

Added feature to classify experimental features in change log. Also fixed an issue with reporting all PRs with missing tags together.

## PR Context
Updates to the script which generates the change log.

tools/releaseTools.psm1

@@ -226,6 +226,9 @@ function Get-ChangeLog
     # Array of PRs tagged with 'CL-Untagged' label.
     $clUntagged = @()
 
+    # Array of PRs tagged with 'CL-Experimental' label.
+    $clExperimental = @()
+
     foreach ($commit in $new_commits) {
         if ($commit.AuthorEmail.EndsWith("@microsoft.com") -or $powershell_team -contains $commit.AuthorName -or $Script:attribution_ignore_list -contains $commit.AuthorEmail) {
             $commit.ChangeLogMessage = "- {0}" -f $commit.Subject
@@ -263,10 +266,10 @@ function Get-ChangeLog
         $clLabel = $pr.labels | Where-Object { $_.Name -match "^CL-"}
 
         if ($clLabel.count -gt 1 -and $clLabel.Name -notcontains 'CL-BreakingChange') {
-            $multipleLabelsPRs = $pr
+            $multipleLabelsPRs += $pr
         }
         elseif ($clLabel.count -eq 0) {
-            $unlabeledPRs = $pr
+            $unlabeledPRs += $pr
         }
         else {
             switch ($clLabel.Name) {
@@ -275,6 +278,7 @@ function Get-ChangeLog
                 "CL-CodeCleanup" { $clCodeCleanup += $commit }
                 "CL-Docs" { $clDocs += $commit }
                 "CL-Engine" { $clEngine += $commit }
+                "CL-Experimental" { $clExperimental += $commit }
                 "CL-General" { $clGeneral += $commit }
                 "CL-Test" { $clTest += $commit }
                 "CL-Tools" { $clTools += $commit }
@@ -302,6 +306,7 @@ function Get-ChangeLog
     PrintChangeLog -clSection $clUntagged -sectionTitle 'UNTAGGED - Please classify'
     PrintChangeLog -clSection $clBreakingChange -sectionTitle 'Breaking Changes'
     PrintChangeLog -clSection $clEngine -sectionTitle 'Engine Updates and Fixes'
+    PrintChangeLog -clSection $clExperimental -sectionTitle 'Experimental Features'
     PrintChangeLog -clSection $clGeneral -sectionTitle 'General Cmdlet Updates and Fixes'
     PrintChangeLog -clSection $clCodeCleanup -sectionTitle 'Code Cleanup'
     PrintChangeLog -clSection $clTools -sectionTitle 'Tools'