Add help item to bottom of signed out top nav

• Requirements (issue)
• Tasks (epic)
• Full Context Spike MR (permanent draft)
• All MR parts ...
  • Add help item to bottom of signed out top nav

What does this MR do?

In the top nav redesign, we identified that we wanted to keep the "Help" accessible for signed out users.

#301143 (comment 561841810)

Screenshots (strongly suggested)

How to test?

• Make sure you have :combined_menu feature flag enabled
• DO NOT SIGN IN
• Visit a page like /explore

Does this MR meet the acceptance criteria?

Conformity

• [ ] I have included a changelog entry, or it's not needed. (Does this MR need a changelog?) not needed since behind feature flag
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)

Related to #301143 (closed)