nixos/prometheus: add fallback_scrape_protocol and scrape_protocols options

I chose to not constrain them to the supported values to be more flexible in supporting any
newly added values. But maybe it makes sense to constrain them, I'm not completely sure.

Ran into this because Prometheus 3.0 was introduced last week and my config broke,
since rtl_433 doesn't set the headers / content-type correctly.

Related-to: https://github.com/NixOS/nixpkgs/pull/358862
Related-to: https://github.com/prometheus/prometheus/pull/15136

nixos/modules/services/monitoring/prometheus/default.nix

@@ -274,6 +274,7 @@ let
     };
   };
 
+  # https://prometheus.io/docs/prometheus/latest/configuration/configuration/#scrape_config
   promTypes.scrape_config = types.submodule {
     options = {
       authorization = mkOption {
@@ -299,6 +300,15 @@ let
         globally configured default.
       '';
 
+      scrape_protocols = mkOpt (types.listOf types.str) ''
+        The protocols to negotiate during a scrape with the client.
+      '';
+
+      fallback_scrape_protocol = mkOpt types.str ''
+        Fallback protocol to use if a scrape returns blank, unparseable, or otherwise
+        invalid Content-Type.
+      '';
+
       metrics_path = mkDefOpt types.str "/metrics" ''
         The HTTP resource path on which to fetch metrics from targets.
       '';