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

services/p2pool.nix

@@ -4,9 +4,6 @@
   lib,
   ...
 }:
-let
-  walletAddress = lib.strings.trim (builtins.readFile ../secrets/xmrig-wallet);
-in
 {
   imports = [
     (lib.serviceMountWithZpool "p2pool" service_configs.zpool_ssds [
@@ -20,7 +17,7 @@ in
   services.p2pool = {
     enable = true;
     dataDir = service_configs.p2pool.dataDir;
-    walletAddress = walletAddress;
+    walletAddress = service_configs.p2pool.walletAddress;
     sidechain = "nano";
     host = "127.0.0.1";
     rpcPort = service_configs.ports.public.monero_rpc.port;