Add Linode to Cloud provider list for hosting options.

What does this MR do?

Add Linode to Cloud Providers list in GitLab install docs.

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because this is a docs only change.
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

This MR should not require any further testing.

Security

This MR does not pose a security risk