[DS-875] Make the main page header and the Virtual Y header sticky to the top for pages that uses Layout Builder

[aleevas]

DS-875

PLEASE CHECK BASE BRANCH FOR YOUR PR ONLY urgent and approved fixes for point release should go to master branch

(Replace this line with a link to the related GitHub issue on YCloudYUSA/yusaopeny_gated_content or your own ticketing system)

Steps to test:

• [ ] log in as admin
• [ ] create a Landing page (LB) > open Layout Builder
• [ ] add Virtual Y Content block to the page > save the page
• [ ] as an anonymous user open the site
• [ ] click on the Enter button
• [ ] open page that you created and compare menus behaviour to the old pages

Quality checks:

Please check these boxes to confirm this PR covers the following cases:

• Maintaining our upgrade path is essential. Check one or the other:
  • [ ] This PR provides updates via hook_update_N or other means.
  • [ ] No updates are necessary for this change.
• Front end fixes should be tested against all of the Open Y Themes.
  • [ ] Tested against Carnation
  • [ ] Tested against Lily
  • [ ] Tested against Rose
  • [ ] This change does not contain front-end fixes.
• [ ] I have flagged this PR "Needs Review" or pinged the VY devs/QA team in Slack