WIP: Make sure SmartInterval is mocked in test

What does this MR do?

Mock SmartInterval in Karma tests.

Also introduces helper function to check for production / test environment.

Why was this MR needed?

To avoid repeated failing Ajax requests in the background. See

• SmartInterval.triggerCallback in https://gitlab.com/gitlab-org/gitlab-ce/-/jobs/64941811
• or (some of) [web-server]: 404: /undefined in https://gitlab.com/gitlab-org/gitlab-ce/-/jobs/65029116 for example

Does this MR meet the acceptance criteria?

• Review
  • Has been reviewed by Frontend

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/33715