Document things to consider when adding a new E2E test

When we add a new E2E test there are some things that we need to remember to consider to be sure they'll be successful. It would be good to document them so we don't have to try to remember. Maybe as a Definition of Done for E2E tests?

For example (not an exhaustive list):

• Will the test be able to run in all our test environments?
• Does the test run in a scenario that needs to be added to our pipelines?
• Does the test need admin rights?
• Does the test create anything that will need to be cleaned up afterwards (e.g., does it leave behind groups/projects?)

I'm not sure where the document should go. Maybe a new document linked here: https://docs.gitlab.com/ee/development/testing_guide/end_to_end/index.html#how-do-i-write-tests