Perf.slow issuable

Merged jneen requested to merge perf.slow-issuable into master

What does this MR do?

Attempts to improve the performance of issuable creation.

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

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/32844.

Edited by Lin Jen-Shin