E2E test: convert add_list_delete_branches_spec to be API only

What does this MR do and why?

Resolves #414249 (closed)

As discussed in #414026 (comment 1417618987) this E2E test has failed multiple times recently due to minor frontend changes. These frontend components are covered by lower level feature specs. This MR converts this from a UI test to using the git CLI and the GitLab API.

Test steps:

1. Create empty project using GitLab API
2. Create repo and push via git CLI to project
3. add / update / retrieve / delete branch via api
4. Fresh git clone
5. confirm branches are added / updated / deleted

Follow up:

• Ensure test case is updated https://gitlab.com/gitlab-org/gitlab/-/quality/test_cases/347740

How to set up and validate locally

From the gitlab/qa/ dir: bundle install

QA_GITLAB_URL=http://192.168.4.31:3000 bundle exec rspec qa/specs/features/api/3_create/repository/add_list_delete_branches_spec.rb

Where http://192.168.4.31:3000 is the address of your GDK

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.