[DTC] Expand Device Trust Browser Test Coverage

Add extra test cases as a follow up to https://chromium-review.googlesource.com/c/chromium/src/+/4627735.

The new test cases include:
- Unmanaged profile test cases, including a case where user becomes managed mid-test
- Attestation policy level test cases, to ensure correct level of attestation occurred

Bug:b:279627319

Change-Id: Ibced51e626c53f7fbacecbaf879cd91e6ff81d1a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4678086
Reviewed-by: Hamda Mare <hmare@google.com>
Commit-Queue: Zonghan Xu <xzonghan@chromium.org>
Reviewed-by: Sébastien Lalancette <seblalancette@chromium.org>
Code-Coverage: Findit <findit-for-me@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1170793}