Make the design management LFS placeholder dismissible

Problem to solve

As a user who doesn't want to enable LFS, I want to dismiss the design management text so I can reduce the visual clutter in issues.

Currently the the page shows a persistent info about LFS;

We want it to become a dismissible alert as mentioned in the attached design of this issue.

Proposal

Make the LFS placeholder message dismissible. Use the recommended Pajamas component (banner). Once dismissed, don't show it again for that user, even on new issues.