Update gitlab.yml.example to match the default settings for Geo sync workers

What does this MR do?

Updates gitlab.yml.example to be in sync with omnibus and config/initializers/1_settings.rb, which looks like:

Settings.cron_jobs['geo_repository_sync_worker'] ||= Settingslogic.new({})
Settings.cron_jobs['geo_repository_sync_worker']['cron'] ||= '*/1 * * * *'
Settings.cron_jobs['geo_repository_sync_worker']['job_class'] ||= 'Geo::RepositorySyncWorker'
Settings.cron_jobs['geo_file_download_dispatch_worker'] ||= Settingslogic.new({})
Settings.cron_jobs['geo_file_download_dispatch_worker']['cron'] ||= '*/1 * * * *'
Settings.cron_jobs['geo_file_download_dispatch_worker']['job_class'] ||= 'Geo::FileDownloadDispatchWorker'

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Without this change, GDK and install-from-source installations will behave differently from omnibus installations with respect to how frequently these cronjobs run.

The intent is that they should run as frequently as possible to keep the gap between runs as short as possible. If a Geo::FileDownloadDispatchWorker or Geo::RepositorySyncWorker job is already running, the new cronjob will exit immediately, so this doesn't represent a large workload.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together