nixos/oauth2_proxy: add missing oidc providers (#165000)

- Add adfs and keycloak-oidc providrs
- Sort the list alphabetically

(cherry picked from commit eef56691e3)

Co-authored-by: Benjamin Staffin <benley@gmail.com>

nixos/modules/services/security/oauth2_proxy.nix

@@ -102,17 +102,19 @@ in
     # Taken from: https://github.com/oauth2-proxy/oauth2-proxy/blob/master/providers/providers.go
     provider = mkOption {
       type = types.enum [
-        "google"
+        "adfs"
         "azure"
+        "bitbucket"
+        "digitalocean"
         "facebook"
         "github"
-        "keycloak"
         "gitlab"
+        "google"
+        "keycloak"
+        "keycloak-oidc"
         "linkedin"
         "login.gov"
-        "bitbucket"
         "nextcloud"
-        "digitalocean"
         "oidc"
       ];
       default = "google";