Move Admin Appearance spinach feature to rspec

What does this MR do?

Replace the Spinach specs for admin appearance with RSpec feature specs as per #23036 (closed)

Are there points in the code the reviewer needs to double check?

Before the feature tested for //img[@src="/uploads/appearance/logo/1/dk.png to be displayed when the logo was added, and then for //img[@src="/uploads/appearance/logo/1/gitlab_logo.png"] to check that it was removed. I think this was a mistake so there was actually no tested path for the removal of the logo.

I have replaced the xpath match with a have_css matcher because it looks like the spinach features cleared the database for each test, so the upload would always get an id of 1 in the path (/logo/1/dk.png), however it looks like the RSpec suite doesn't clear the DB in the same way, so the upload will end up as /logo/2/dk.png. I believe we're still testing for wether or not the logo is displayed on the page, so we should be good.

Does this MR meet the acceptance criteria?

• [-] Changelog entry added
• [-] Documentation created/updated
• [-] API support added
• Tests
  • [-] Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

#23036 (closed)