Prepare partitioning constraint for ci_stages
Ref: #428988 (closed)
What does this MR do and why?
This MR enqueues a job which will create a new constraint this weekend on ci_stages
for gitlab.com.
This is a similar approach we used for ci_job_artifacts
in !142648 (merged).
Why are we doing this?
This is a prerequisite in order to partition this table.