hst: expose scheduling policy

This is primarily useful for poorly written music players for now.

Signed-off-by: Ophestra <cat@gensokyo.uk>

options.nix

@@ -98,6 +98,7 @@ in
               ints
               str
               bool
+              enum
               package
               anything
               submodule
@@ -237,6 +238,22 @@ in
               };
               hostAbstract = mkEnableOption "share abstract unix socket scope";
 
+              schedPolicy = mkOption {
+                type = nullOr (enum [
+                  "fifo"
+                  "rr"
+                  "batch"
+                  "idle"
+                  "deadline"
+                  "ext"
+                ]);
+                default = null;
+                description = ''
+                  Scheduling policy to set for the container.
+                  The zero value retains the current scheduling policy.
+                '';
+              };
+
               nix = mkEnableOption "nix daemon access";
               mapRealUid = mkEnableOption "mapping to priv-user uid";
               device = mkEnableOption "access to all devices";