MediaService: Add MediaBackendError

This get's thrown when the backend can't perform the required action.

Signed-off-by: Philip Molares <philip.molares@udo.edu>

src/errors/errors.ts

@@ -31,3 +31,7 @@ export class TooManyTokensError extends Error {
 export class PermissionsUpdateInconsistentError extends Error {
   name = 'PermissionsUpdateInconsistentError';
 }
+
+export class MediaBackendError extends Error {
+  name = 'MediaBackendError';
+}