Geo - Redirect user back to the secondary after a logout & re-login via the primary

What does this MR do?

When you log out from a secondary node, it takes you to the primary login screen. However logging in again will log the user into the primary and not redirect it back to the secondary.

The changes in this MR redirect the user back to the secondary node when the user logs out from the secondary and then log in into the primary.

What are the relevant issue numbers?

Closes #4459 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• ~~Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.~~
• EE specific content should be in the top level /ee folder
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?

/cc @brodock