Use unique user accounts for e2e Cypress tests

[bourgeoisor]

Currently, the Cypress e2e tests creates predefine user accounts to run tests and then deletes them. This can fail through race conditions if multiple instances of these tests are running simultaneously against the same cluster (for example, if we trigger multiple Cloud Deploy promotions at the same time). We should investigate if we can generate user accounts that would be unique per-instance of Cypress.

[bourgeoisor]

This is still important to do.