Add a base test for adding a new branch rule

Description of the test

Adds a base E2E test to verify a happy path flow for the new Branch Rules section, see gitlab-org/quality/quality-engineering/team-tasks#1663 (closed).

Open Settings/Repository/Branch Rules -> Click Add Branch Rule -> Create Protected Branch with Merge and Push rules -> Verify Branch Rules displayed on Details page

How to set up and validate locally

From the qa directory:

bundle install
export WEBDRIVER_HEADLESS=false # If you'd like to watch the test in action
export QA_GITLAB_URL="http://gdk.test:3000" # Only needed if GDK is not running on http://127.0.0.1:3000
bundle exec rspec qa/specs/features/browser_ui/3_create/repository/add_new_branch_rule_spec.rb

Checklist

• Confirm the test has a testcase: tag linking to an existing test case in the test case project.
• Note if the test is intended to run in specific scenarios. If a scenario is new, add a link to the MR that adds the new scenario.
• Follow the end-to-end tests style guide and best practices.
• Use the appropriate RSpec metadata tag(s).
• Most resources will be cleaned up via the general cleanup task. Check that is successful, or ensure resources are cleaned up in the test:
  • New resources have api_get_path and api_delete_path implemented if possible.
  • If any resource cannot be deleted in the general delete task, make sure it is ignored.
  • If any resource cannot be deleted in the general delete task, remove it in the test (e.g., in an after block).
• Ensure that no transient bugs are hidden accidentally due to the usage of waits and reloads.
• Verify the tags to ensure it runs on the desired test environments.
• If this MR has a dependency on another MR, such as a GitLab QA MR, specify the order in which the MRs should be merged.
• (If applicable) Create a follow-up issue to document the special setup necessary to run the test: ISSUE_LINK
• If the test requires an admin's personal access token, ensure that the test passes on your local environment with and without the GITLAB_QA_ADMIN_ACCESS_TOKEN provided.