Add HTML anchors to Top Annual Contributors page

Why is this change being made?

This MR allows linking to a specific year of the Top Annual Contributors page through the use of HTML anchors so that users can jump directly to a particular section with hyperlinks

By appending #2019 to the base URL of the Top Annual Contributors page (https://about.gitlab.com/community/top-annual-contributors/), we get https://about.gitlab.com/community/top-annual-contributors/#2019 which links to the 2019 top annual contributors

This MR allows linking to the 2018, 2019, and 2020 top annual contributors section by appending #2018, #2019, and #2020 to the URL, respectively

Author Checklist

• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
  • Copy/paste the Slack conversation to document it for later, or upload screenshots. Verify that no confidential data is added.
• Assign reviewers for this change to the correct DRI(s)
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the "Maintained by" section in on the page being edited.
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies.

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