Fix scrollbar layout shift on all pages

Summary:
Apply scrollbar-gutter: stable to html element via Tailwind plugin
to prevent layout shift when scrollbars appear/disappear.

Closes T2270

Reviewers: ieli

Reviewed By: ieli

Subscribers: Chenani-MohamedAmine

Maniphest Tasks: T2270

Differential Revision: https://devcentral.nasqueron.org/D3997