[e2e-examiner-ui] Examiner: BCeID available for e2e testing only

## Summary

Examiner web application must accept BCeID-based sessions for automated end-to-end testing, without presenting BCeID as a normal, user-facing login choice for the production-like Examiner experience. This will be used exclusively for e2e testing and conditionals must be placed in order to prevent unauth access.

## Proposed Solution
- use the route /auth/login?idp=bceid to allow e2e testing to complete a BCeID-backed login path.
- no login button or link to BCeID should be present in the primary login experience.
- ensure that the primary login experience remains appropriate for the intended audience (no unintended BCeID entry point for typical users).