Rename the ENV to match standard

In order to match the current naming standard in the ENVs that control the configuration of the Cardano DBSync docker service this commit changes the name of the ENV responsible for config file to `DB_SYNC_CONFIG`.

Author: placek

nix/nixos/cardano-db-sync-service.nix

@@ -217,7 +217,7 @@ in {
               LEDGER_OPTS="--state-dir ${cfg.stateDir}"
             fi
 
-            if [[ -z "''${CARDANO_DB_SYNC_CONFIG:-}" ]]; then
+            if [[ -z "''${DB_SYNC_CONFIG:-}" ]]; then
               exec ${exec} \
                   --config ${configFile} \
                   --socket-path "$CARDANO_NODE_SOCKET_PATH" \
@@ -227,7 +227,7 @@ in {
                   ''${EXTRA_DB_SYNC_ARGS:-}
             else
               exec ${exec} \
-                  --config "$CARDANO_DB_SYNC_CONFIG" \
+                  --config "$DB_SYNC_CONFIG" \
                   --socket-path "$CARDANO_NODE_SOCKET_PATH" \
                   --schema-dir ${self.schema} \
                   ${toString cfg.rtsArgs} \