E2E - Update CI file with pipeline editor

Description of the test

New E2E test using pipeline editor to submit changes to CI config file. User can set a new target branch that hasn't existed yet while editing the file content. When submit changes (click Commit changes button on the page):

• The editor content remains the same with the changed content
• The target branch field remains the same with the new target branch name
• The branch switch button is now changed to the new target branch instead of main/default branch
• A new pipeline is created and reflected on the page without refreshing
• The target branch is actually created (it is now one of the project's branches)

Test case https://gitlab.com/gitlab-org/gitlab/-/quality/test_cases/349005

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).
• Ensure that a created resource is removed after test execution. A Group resource can be shared between multiple tests. Do not remove it unless it has a unique path. Note that we have a cleanup job that periodically removes groups under gitlab-qa-sandbox-group.
• 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.