Add columns about MR checks to namespace_settings
Related issue: #372040 (closed) & &8704 (closed)
What does this MR do and why?
Add three columns to the table namespace_settings to support users to configure MR checks at the group level.
- only_allow_merge_if_pipeline_succeeds
- allow_merge_on_skipped_pipeline
- only_allow_merge_if_all_discussions_are_resolved
cc @prajnamas
Edited by Zhiyuan Lu