fix(ha): read transcode store config from the variable form deployments set

The startup configuration only reads JELLYFIN_ prefixed environment
variables, so the bare Jellyfin__TranscodeStore__* form used by the chart,
the manifests and the README is dropped and the Redis store is never
registered. Nothing logs the selected store, so the fallback is invisible.

- Read bare Jellyfin__* variables into the Jellyfin:* configuration root
- Keep an explicit JELLYFIN_ variable winning over the bare form
- Log the selected transcode session store at startup
- Ping Redis once at startup and log an unreachable store at Error
- Log endpoints only, never the connection string

MediaBrowser.Controller/MediaEncoding/TranscodeStoreOptions.cs

@@ -5,6 +5,16 @@ namespace MediaBrowser.Controller.MediaEncoding;
 /// </summary>
 public sealed class TranscodeStoreOptions
 {
+    /// <summary>
+    /// The configuration section these options bind from.
+    /// </summary>
+    public const string ConfigurationSection = "Jellyfin:TranscodeStore";
+
+    /// <summary>
+    /// The configuration key holding the Redis connection string.
+    /// </summary>
+    public const string RedisConnectionStringKey = ConfigurationSection + ":RedisConnectionString";
+
     /// <summary>
     /// Gets or sets the Redis connection string.
     /// A <c>null</c> or empty value indicates single-instance mode, where