Add GitLab 14 Community meetup video as resource to about.gitlab.com/gitlab-14/

Why is this change being made?

The community meetup for GitLab 14 video provides helpful insights into the features from 13 => 14, with a personal view & live demos from wider community members and Developer Evangelists.

This MR adds the video as SSoT resource into https://about.gitlab.com/gitlab-14/ - it has timestamps to scroll fast, and links the slides too.

Discussed in https://gitlab.com/gitlab-com/marketing/community-relations/evangelist-program/general/-/issues/1199#note_614815648 with @williamchia

Related to gitlab-com/marketing/corporate_marketing&52 (closed)

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
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/cc @gitlab-de @dplanella @melsmo