chore(deps): update dependency fluentd to v1.18.0 (#15185)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

clients/cmd/fluentd/docker/Gemfile

@@ -2,5 +2,5 @@
 
 source 'https://rubygems.org'
 
-gem 'fluentd', '1.17.1'
+gem 'fluentd', '1.18.0'
 gem 'fluent-plugin-multi-format-parser', '~>1.1.0'