Sync config v14.3.0 : Update comment: default gitlab-shell log format is "json"

This commit is imported from upstream.
For more detail, check corresponding merge request:
https://gitlab.com/gitlab-org/gitlab-shell/-/merge_requests/476

First contain : gitlab-shell v13.21.0
Corresponding gitlab v14.3.0

Author: kkimurak

assets/runtime/config/gitlab-shell/config.yml

@@ -54,7 +54,7 @@ log_file: "{{GITLAB_LOG_DIR}}/gitlab-shell/gitlab-shell.log"
 # Log level. INFO by default
 log_level: INFO
 
-# Log format. 'text' by default
+# Log format. 'json' by default, can be changed to 'text' if needed
 # log_format: json
 
 # Audit usernames.