Change DuplicateJobs cookie key
Part of gitlab-com/gl-infra/scalability#1954 (closed).
This is follow-up to !102578 (closed).
In !101925 (merged) we changed the format of DuplicateJobs cookies in a breaking way. This was feature flagged but in local tests, feature flags are enabled by default. What we should have done when we changed the format was to also change the Redis keys, so that new code cannot read old cookies. This MR changes the cookie key.
Edited by Jacob Vosmaer