Docs: GL Pages - replace forking with project templates

Type of issue

Update documentation.

Problem to solve

Update Pages' getting started section to show the new project templates instead of forking a project.

Proposal

Update according to the new feature bundled templates for Pages.

Who can address the issue

@marcia @jlenny

Other links/references

• Added to https://gitlab.com/gitlab-org/gitlab-ce/issues/39978
• Docs introduced in GL 11.8: https://gitlab.com/gitlab-org/gitlab-ce/commit/0f355e57f60cb52bb68c624807121a84a20d32dc // https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/24796
• Feature introduced by https://gitlab.com/gitlab-org/gitlab-ce/issues/47857