Enable ci_config_merged_tab feature by default
What does this MR do?
Enable ci_config_merged_tab
feature flag by default and adds the changelog.
Screenshots (strongly suggested)
Does this MR meet the acceptance criteria?
Conformity
Availability and Testing
Merged tab is contained on its own and should it breaks, it would mean that the content of the tab would be empty. There is a default error state that would catch this. So far on multiple projects, it works as intended.