Updated Handbook Favicon/Logo

New Handbook and time for an updated Logo/Favicon. I don't have access to the original svg files for the public handbook and I feel it would be nice to update the Gitlab logo used on the favicon to the latest iteration. In addition to this we have just landed new favicons and logos for the internal handbook and it would be get these in sync.

This favicon should be ideally: Purple 01p (#A989F5) with a large white GitLab logo on it. The handbook doesn't feature the lock of the internal handbook.

For the Internal Handbook see: https://gitlab.com/internal-handbook/internal-handbook.gitlab.io/-/issues/37

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