Add sentry_clientside_traces_sample_rate setting to gon

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/130144



Merged-by: Terri Chu <tchu@gitlab.com>
Approved-by: Radamanthus Batnag <rbatnag@gitlab.com>
Approved-by: Terri Chu <tchu@gitlab.com>
Reviewed-by: Terri Chu <tchu@gitlab.com>
Reviewed-by: Sheldon Led <sheldonled@gitlab.com>
Reviewed-by: Radamanthus Batnag <rbatnag@gitlab.com>
Co-authored-by: Sheldon Led <sheldonled@gitlab.com>