Introduce Corporate Communications sub-team; update Integrated Marketing in the marketing handbook, part 2

Why is this change being made?

Note: This MR is based on !115464 (merged) and requires it being merged prior.

Apply changes from the marketing reorganization tasks in #13991 (closed)

• Move Corporate Communications into /handbook/marketing handbook
• Update Integrated Marketing landing page
• Move Corporate Events to Integrated Marketing
• Move Digital Strategy into Integrated Marketing
• Move Social Marketing into Integrated Marketing > Digital Strategy
• Update redirects and CODEOWNERS
• Update names and titles

Note: The integrated marketing/corporate communications handbook and sub-pages need a separate review for consistency and accuracy from DRIs; this is out of scope for reorganizing the structure and adding basic color to the handbook.

Review App URLs

• Main marketing page
  • Integrated Marketing: https://reorg-marketing-handbook-2.about.gitlab-review.app/handbook/marketing/#integrated-marketing
  • Corporate Communications: https://reorg-marketing-handbook-2.about.gitlab-review.app/handbook/marketing/#corporate-communications
• Integrated Marketing handbook: https://reorg-marketing-handbook-2.about.gitlab-review.app/handbook/marketing/integrated-marketing/
  • Corporate Events: https://reorg-marketing-handbook-2.about.gitlab-review.app/handbook/marketing/integrated-marketing/corporate-events/
  • Digital Strategy: https://reorg-marketing-handbook-2.about.gitlab-review.app/handbook/marketing/integrated-marketing/digital-strategy/
  • Social Marketing: https://reorg-marketing-handbook-2.about.gitlab-review.app/handbook/marketing/integrated-marketing/digital-strategy/social-marketing/
• Corporate Communications handbook: https://reorg-marketing-handbook-2.about.gitlab-review.app/handbook/marketing/corporate-communications/
  • Speaking resources: https://reorg-marketing-handbook-2.about.gitlab-review.app/handbook/marketing/corporate-communications/speaking-resources/

Author Checklist

• Provided a concise title for this Merge Request (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 MR to the correct Directly Responsible Individual/s (DRI)
  • 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 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
• If the changes affect team members, or warrant an announcement in another way, please consider posting an update in #whats-happening-at-gitlab linking to this MR
  • If this is a change that directly impacts the majority of global team members, it should be a candidate for #company-fyi. Please work with internal communications and check the handbook for examples.

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