Add conditions for triggering end-to-end tests

This is another iteration of the work being done as part of #110 (closed)

There were a lot of end-to-end test pipelines being triggered due to the feature flags being toggled in quick succession for different groups causing a lot of noise on the #qa-staging and #qa-production slack channels.

We do not need to run the end-to-end tests when a feature flag is turned on for a specific user or a group or a project with the exception of the gitlab-qa user and the gitlab-qa-sandbox-group. Also, the end-to-end tests will not run when a feature is switched on for anything other than 100% of the time/users.

The end-to-end tests will be triggered if no user, project or group is specified.