Refactor ce landing page

Closing in favour of: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/23215.

What does this MR do?

As part of https://gitlab.com/gitlab-org/gitlab-ce/issues/52304, a revamped CE landing page was developed and merged in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21946.

Unfortunately, a few tests broken because they relied on the old structure and were only run post-deploy. That meant the new content was reverted: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/23179.

This MR is a do-over, with a full pipeline and fixed test.

Related issues

None beyond those mentioned above.

Author's checklist

• Apply the correct labels and milestone
• Port the MR to EE (or backport from CE): always recommended, required when the ee-compat-check job fails

Review checklist

• Your team's review (required)
• PM's review (recommended, but not a blocker)
• Technical writer's review (required)
• Merge the EE-MR first, CE-MR afterwards