Added support for selenium UI testing with Firefox

Paulrequested to merge
feature/add-selenium-testing into feature/upgrade-hyrax-to-v5

fixes https://github.com/antleaf-user/reseed/issues/40

  1. Added Firefox binary (firefox-esr) to Dockerfile
  2. Added support for selenium testing with a headless firefox browser to rspec
  3. Added a basic selenium test for homepage to prove this works
Edited by Anusha Ranganathan

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