Support github user namespaces for codespaces environments (Azure#20218)

Co-authored-by: Ben Broderick Phillips <bebroder@microsoft.com>

Author: azure-sdk

eng/common/scripts/stress-testing/find-all-stress-packages.ps1

@@ -45,9 +45,18 @@ function NewStressTestPackageInfo([hashtable]$chart, [System.IO.FileInfo]$chartF
     $namespace = if ($CI) {
         $chart.annotations.namespace
     } else {
-        $namespace = if ($env:USER) { $env:USER } else { "${env:USERNAME}" }
-        # Remove spaces, etc. that may be in $namespace
-        $namespace -replace '\W'
+        # Check GITHUB_USER for users in codespaces environments, since the default user is `codespaces` and
+        # we would like to avoid namespace overlaps for different codespaces users.
+        $namespace = if ($env:GITHUB_USER) {
+            $env:GITHUB_USER
+        } elseif ($env:USER) {
+            $env:USER
+        } else {
+            $env:USERNAME
+        }
+        # Remove spaces, underscores, etc. that may be in $namespace. Value must be a valid RFC 1123 DNS label:
+        # https://kubernetes.io/docs/concepts/overview/working-with-objects/names/#dns-label-names
+        $namespace -replace '_|\W', '-'
     }
 
     return [StressTestPackageInfo]@{