update docs

Author: skudasov

book/src/framework/configuration.md

@@ -12,3 +12,4 @@
 |       LOKI_BASIC_AUTH        |                                                          Basic auth in format $user:$password                                                          |        `$user:$password` |                          -                          |    🚫     |
 |         RESTY_DEBUG          |                                                            Log all Resty client HTTP calls                                                             |          `true`, `false` |                       `false`                       |    🚫     |
 |   CTF_IGNORE_CRITICAL_LOGS   |                                      Ignore all logs that has CRIT,FATAL or PANIC levels (Chainlink nodes only!)                                       |          `true`, `false` |                       `false`                       |    🚫     |
+|       CHAINLINK_IMAGE        |                                           Flag to override Chainlink Docker image in format $repository:$tag                                           |         $repository:$tag |                          -                          |    🚫     |