Change `ci_pipeline_creation_step_duration_tracking` feature flag to ops type

Context

The ci_pipeline_creation_step_duration_tracking feature flag was added in !68485 (merged). It is currently enabled by default. Initially, its purpose was to allow an easy way to disable the pipeline creation step histogram because a situation happened previously where there was a mistake with the labels in a histogram that created problems with Prometheus. However, we have discovered that that there is a significant rate of observations done (10-15 pipelines per second multiplied by 22 pipeline creation steps on GitLab.com), and we know that this histogram is not very useful for users who run their own instances. Therefore, we want to update the feature flag to better serve us.

Technical details

• Change the ci_pipeline_creation_step_duration_tracking feature flag type to ops
• Update the flag to be disabled by default
• Ensure the flag is enabled on gitlab.com