Draft: GitLab is PascalCase, updating all references

Why is this change being made?

The following wording on our Writing style guidelines states:

Always write "GitLab" with "G" and "L" capitalized, even when writing "GitLab.com", except within URLs. When "gitlab.com" is part of a URL it should be lowercase.

the trouble is, even on that page there's Gitlab instead of GitLab:

Extend and strengthen Gitlab Values, Mission and Culture to Core Team while maintaining compliance as a publicly traded company

This merge request aims to ensure we follow our writing style as inconsistencies may have an impact on GitLab the brand.

Slack thread with discussion is in the #handbook slack channel.

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, and the content is SAFE
• 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
  • The when to get approval handbook section explains the workflow in more detail
• 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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