Add .CRT extension to Certificate Encoder / Decoder (#887)

Author: veler

src/dev/impl/DevToys/ViewModels/Tools/EncodersDecoders/CertificateEncoderDecoder/CertificateEncoderDecoderToolViewModel.cs

@@ -32,6 +32,7 @@ public class CertificateEncoderDecoderToolViewModel : ObservableRecipient, ITool
         private readonly ImmutableHashSet<string> _allowedFileExtensions = new HashSet<string>()
         {
             ".cer",
+            ".crt",
             ".pfx",
             ".pem"
         }.ToImmutableHashSet();