UNIVERSAL_PROXY_CONFIG_URL env variable (#409)

Author: vbaranov

setup/env-variables/backend-env-variables.md

@@ -100,6 +100,7 @@ _**Note**_**: Before release 5.1.2, all environment variables of time format sup
 | `PUBLIC_METRICS_UPDATE_PERIOD_HOURS`                    | Public metrics update period in hours at /public-metrics endpoint. Implemented in [#10469](https://github.com/blockscout/blockscout/pull/10469).                                                                                                                                                                                                                                                                                                   | <p>Version: v6.8.0+<br>Default: 24<br>Applications: API</p>                                                                                                                |
 | `SHRINK_INTERNAL_TRANSACTIONS_ENABLED`                  | Variable to enable internal transactions shrinking logic. Implemented in [#10567](https://github.com/blockscout/blockscout/pull/10567).                                                                                                                                                                                                                                                                                                            | <p>Version: v6.8.0+<br>Default: <code>false</code><br>Applications: API, Indexer</p>                                                                                       |
 | `HACKNEY_DEFAULT_POOL_SIZE`                             | Size of `default` hackney pool. Implemented in [#12406](https://github.com/blockscout/blockscout/pull/12406).                                                                                                                                                                                                                                                                                                                                      | <p>Version: v8.1.0+<br>Default: <code>1000</code><br>Applications: API, Indexer</p>                                                                                         |
+| `UNIVERSAL_PROXY_CONFIG_URL`                             | Config URL for universal proxy. Implemented in [#12442](https://github.com/blockscout/blockscout/pull/12442).                                                                                                                                                                                                                                                                                                                                      | <p>Version: v8.1.0+<br>Default: <code>https://raw.githubusercontent.com/blockscout/backend-configs/refs/heads/main/universal-proxy-config.json</code><br>Applications: API</p>                                                                                         |
 
 ## <mark style="background-color:orange;">Indexer Management</mark>