Blog to update security trends in GitLab-hosted projects

Closes #8996 (closed)

Checklist for writer

• Link to issue added, and set to close when this MR is merged #8996 (closed)
• Due date and milestone (if applicable) added for the desired publish date
• Please add links to three related blog posts, GitLab issues, documentation or other related content so the reader can learn more at the bottom of the post. (We will take care of the formatting.)
• If time sensitive
  • Added ~"priority" label
  • Mentioned @rebecca to give her a heads up ASAP
• Blog post file formatted correctly, including any accompanying images
• All relevant frontmatter included
• Review app checked for any formatting issues
• Reviewed by fellow team member
• If approval before publishing is required
  • Any required internal or external approval for this blog post has been granted (please leave a comment with details)
• Assign to @rebecca for review

Wayne's final checklist

• Ask fellow team member(s) to review content. Ask for feedback by Tue, Sep 29.
• After feedback is received by one, assign to Rebecca for review on or before Wed, Sep 30 (4 business days before blog publishing date)
• Reread all content forwards and backwards one more time
• Check all links
• Confirm background image is displaying properly
• Compress all images
• Fix image links

Review app direct link: https://whaber-october-2020-security-trends-blog.about.gitlab-review.app/blog/2020/10/06/gitlab-latest-security-trends/index.html

Ref: https://gitlab.com/gitlab-com/marketing/corporate_marketing/corporate-marketing/-/issues/3392