feat(dgw): support .cast terminal recording files (#900)

The .cast extension is used for "asciicast" files, i.e.: asciinema cast files.
This is a widely used terminal playback format.

Co-authored-by: Benoît Cortier <bcortier@proton.me>

devolutions-gateway/src/token.rs

@@ -262,13 +262,16 @@ pub enum RecordingFileType {
     WebM,
     /// Terminal Playback
     TRP,
+    /// asciinema cast for terminal playback
+    Asciicast,
 }
 
 impl RecordingFileType {
     pub const fn as_str(self) -> &'static str {
         match self {
             RecordingFileType::WebM => "webm",
             RecordingFileType::TRP => "trp",
+            RecordingFileType::Asciicast => "cast",
         }
     }
 }