Add a setting to enable display of pipeline variables

Problem

Following the implementation of #323097 (closed)

We've received feedback from some of our users that would like to disable this feature

Proposal

Adding a setting in the UI that enable this feature, once a user enable the feature a warning pops up mentioning that some users may be adding secrets in a manual variable which now will be visible in the UI

This setting will be available for project owners only

UPDATED 2025: This issue is for the BE and FE work, which might or might not be in the same MR.