[DOCS] Add reference to ECS-reformatting configuration

[eyalkoren]

Closes elastic/ecs-logging-java#176

[apmmachine]

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#### Build stats * Start Time: 2022-04-28T13:04:15.102+0000 * Duration: 7 min 10 sec #### Test stats :test_tube: | Test | Results | | ------------ | :-----------------------------: | | Failed | 0 | | Passed | 232 | | Skipped | 0 | | Total | 232 |

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