Allow hiding repository features

We need the option to completely hide UI buttons in the repo's sidebar. For example, we should be able to hide:

• Pipelines
• Deployments
• Boards

This has many benefits:

1. It allows you to keep the repo clean and simple in case you don't use these features (e.g you use alternatives)
2. It keeps your users (e.g. employees) from accidentally enabling/using these features, against company policy.

I can understand Atlassian wanting to promote their features, but things can get cluttered and some people could appreciate the control and simplicity. In my opinion, this is one of the few areas where GitLab still holds the advantage, as it allows you to easily turn UI features on/off.