Binary Transparency: Log sepolicy hash

The telemetry can help us detect divergence in the field.

Also log vbmeta digest in the new atom. Later we will deprecate
VbmetaDigestReported.

Bug: 308471499
Test: set flag to false; doesn't see hash in the log
Test: set flag to tree; does see hash in the log
Change-Id: I5fbadb5345d7b2dec67d43daa83f43f41ebde655