Correct project name/group name limitations

What does this MR do?

Project and group names DO NOT have to start and end with a letter (a-zA-Z) or a digit (0-9).

• The only limitation on project names are:
  • Project names can contain only letters (a-zA-Z), digits (0-9), emoji, underscores (_), dots (.), pluses (+), dashes (-), or spaces.
• The only limitation on group names are:
  • Group names can contain only letters (a-zA-Z), digits (0-9), emoji, underscores (_), dots (.), parentheses (()), dashes (-), or spaces.

However, the slug/path of projects and group:

• Must start with a letter (a-zA-Z) or digit (0-9).
• Must not contain consecutive special characters.
• Cannot start or end with a special character.
• Cannot end in .git or .atom.
• Can contain only letters (a-zA-Z), digits (0-9), underscores (_), dots (.), or dashes (-).

Customers are confusing the limitations on the name and the slug. Is there a better way to clarify the name and slug differences.

Related issues

https://gitlab.zendesk.com/agent/tickets/556257

Author's checklist

• Optional. Consider taking the GitLab Technical Writing Fundamentals course.
• Follow the:
  • Documentation process.
  • Documentation guidelines.
  • Style Guide.
• If you're adding a new page, add the product availability details under the H1 topic title.
• If you are a GitLab team member, request a review based on:
  • The documentation page's metadata.
  • The associated Technical Writer.

If you are a GitLab team member and only adding documentation, do not add any of the following labels:

• ~"frontend"
• ~"backend"
• ~"type::bug"
• ~"database"

These labels cause the MR to be added to code verification QA issues.

Reviewer's checklist

Documentation-related MRs should be reviewed by a Technical Writer for a non-blocking review, based on Documentation Guidelines and the Style Guide.

If you aren't sure which tech writer to ask, use roulette or ask in the #docs Slack channel.

• If the content requires it, ensure the information is reviewed by a subject matter expert.
• Technical writer review items:
  • Ensure docs metadata is present and up-to-date.
  • Ensure the appropriate labels are added to this MR.
  • Ensure a release milestone is set.
  • If relevant to this MR, ensure content topic type principles are in use, including:
    • The headings should be something you'd do a Google search for. Instead of Default behavior, say something like Default behavior when you close an issue.
    • The headings (other than the page title) should be active. Instead of Configuring GDK, say something like Configure GDK.
    • Any task steps should be written as a numbered list.
    • If the content still needs to be edited for topic types, you can create a follow-up issue with the docs-technical-debt label.
• Review by assigned maintainer, who can always request/require the reviews above. Maintainer's review can occur before or after a technical writer review.