Warn about unknown logger fields

What does this MR do and why?

References

• Investigation into Ruby Linter Rules for Fields (gitlab-org/quality/quality-engineering/team-tasks#4033)

Screenshots or screen recordings

$ be rails console
DEPRECATION WARNING: `config.active_record.warn_on_records_fetched_greater_than` is deprecated and will be removed in Rails 8.0. Please subscribe to `sql.active_record` notifications and access the row count field to detect large result set sizes. (called from <main> at /home/peter/devel/gitlab/gdk/gitlab/config/environment.rb:7)
Logger Gitlab::Database::LoadBalancing::Logger emitted unknown fields: ["event", "model", "start_service_discovery"]
Logger Gitlab::Database::LoadBalancing::Logger emitted unknown fields: ["event", "model", "start_service_discovery"]
Logger Gitlab::Database::LoadBalancing::Logger emitted unknown fields: ["event", "model", "start_service_discovery"]
Logger Gitlab::Database::LoadBalancing::Logger emitted unknown fields: ["event", "model", "start_service_discovery"]
Logger Gitlab::AuthLogger emitted unknown fields: ["gitlab_throttle_user_allowlist"]
Logger Gitlab::Database::LoadBalancing::Logger emitted unknown fields: ["event", "model", "start_service_discovery"]
Logger Gitlab::Database::LoadBalancing::Logger emitted unknown fields: ["event", "model", "start_service_discovery"]
--------------------------------------------------------------------------------
 Ruby:         ruby 3.3.9 (2025-07-24 revision f5c772fc7c) [x86_64-linux]
 GitLab:       18.7.0-pre (153f3c5b194) EE
 GitLab Shell: 14.45.3
 PostgreSQL:   16.10
-------------------------------------------------------------[ booted in 7.94s ]

How to set up and validate locally

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