Add service ping config e2e test

What does this MR do and why?

Add some e2e tests for service ping

Possible scenarios we want to test:

In this MR:

• When usage_ping_enabled: false in gitlab.yml file then in admin setting the service ping checkbox should be disabled

Follow up MRs:

• When usage_ping_enabled: true in gitlab.yml file then in admin setting the service ping checkbox should not be disabled
• When usage_ping_enabled: true we can successfully send a service ping to version-app
  • This happens on a regular basis using a worker who posts a JSON payload to version-app

Related MR for adding Service Ping configuration gitlab-qa!788 (diffs)

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MR acceptance checklist

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

New End-to-End test 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 with and without the GITLAB_QA_ADMIN_ACCESS_TOKEN provided.