Show GitLab.com on the help page instead of GitLab Enterprise Edition only for SaaS

What does this MR do?

Show GitLab.com on the help page instead of GitLab Enterprise Edition only for SaaS

I found that a lot of areas under GitLab is specific only for SaaS and also some are available only for self-hosted solutions, here are some examples

SaaS only

Self-hosted only

Also, GitLab CE and EE sounds more like a self-hosted solution but GitLab.com sound more SaaSy

I found that GitHub is sharing the same codebase with GitHub Enterprise Server but the differentiated it well

Source: https://bounty.github.com/targets/github-enterprise-server.html

Closes #299027

Screenshots (strongly suggested)

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Does this MR meet the acceptance criteria?

Conformity

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• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

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