Make feature pages consistent

1. Link to the EE documentation for everything, both on feature and feature details page.
2. On the feature page make all the feature boxes clickable (not just the hover ones).
3. Have a documentation link in the header, nothing else.
4. Have a 'Free trial' link at the bottom, nothing else.
5. Don't link to blog posts.
6. Deprecate https://about.gitlab.com/features/premium-support/
7. Review and add the following features to /features
   1. Time Tracking
   2. Geo
   3. File Locking https://about.gitlab.com/features/gitlab-geo

So for example:

• https://about.gitlab.com/features/gitlab-ci-cd/ => remove comparison link and "Choose the version of GitLab that is best for you | Host GitLab on your servers or let us host it for you" copy
• https://about.gitlab.com/features/pages/ => add explore our products
• https://about.gitlab.com/features/issueboard/ header should not link to a blog post and the video should not be in the header (it is already is listed below)
• https://about.gitlab.com/features/review-apps/ should not link to the blog post