secrets: migrate build-time secrets to agenix runtime

- coturn: switch static-auth-secret to static-auth-secret-file
- matrix: switch registration_token and turn_secret to file-based
- murmur: switch password to environmentFile with agenix
- p2pool: move public wallet address to service-configs.nix

configuration.nix

@@ -290,7 +290,8 @@
     enable = true;
     openFirewall = true;
     welcometext = "meow meow meow meow meow :3 xd";
-    password = builtins.readFile ./secrets/murmur_password;
+    password = "$MURMURD_PASSWORD";
+    environmentFile = config.age.secrets.murmur-password-env.path;
     port = service_configs.ports.public.murmur.port;
   };