Added offline build mode for local build script (#806)

app/Build/Tools/Environment.cs

@@ -7,6 +7,7 @@ namespace Build.Tools;
 public static class Environment
 {
     public const string DOTNET_VERSION = "net9.0";
+    public const string BUILD_OFFLINE_ENVIRONMENT_VARIABLE = "AI_STUDIO_BUILD_OFFLINE";
     public static readonly Encoding UTF8_NO_BOM = new UTF8Encoding(false);
     
     private static readonly Dictionary<RID, string> ALL_RIDS = Enum.GetValues<RID>().Select(rid => new KeyValuePair<RID, string>(rid, rid.AsMicrosoftRid())).ToDictionary(kvp => kvp.Key, kvp => kvp.Value);
@@ -47,6 +48,19 @@ public static class Environment
         return Path.GetFullPath(directory);
     }
 
+    public static bool IsOfflineBuildRequested(bool offlineOption)
+    {
+        if (offlineOption)
+            return true;
+
+        var environmentValue = global::System.Environment.GetEnvironmentVariable(BUILD_OFFLINE_ENVIRONMENT_VARIABLE);
+        return environmentValue?.Trim().ToLowerInvariant() switch
+        {
+            "1" or "true" or "yes" or "on" => true,
+            _ => false,
+        };
+    }
+
     public static string? GetOS()
     {
         if(RuntimeInformation.IsOSPlatform(OSPlatform.Windows))