Increase stable groups for FREMobileIdentityConsistencySynthetic to 10%

This CL adjusts FREMobileIdentityConsistencySynthetic trial:
* Group sizes on Stable are increased from 1% to 10%.
* Groups are renamed to Enabled6, Disabled6 and OldFreWithUmaDialog6.
* FREMobileIdentityConsistencyVariationsSynthetic group sizes on
  Beta are decreased from 10% to 0%. This should improve the reliability
  of Beta data for FREMobileIdentityConsistencySynthetic, as it should
  no longer be affected by the variations trial.

Bug: 1345946
Change-Id: Ic729dd0b13cda677e061165fa318219a66d2de65
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3776621
Commit-Queue: Boris Sazonov <bsazonov@chromium.org>
Auto-Submit: Boris Sazonov <bsazonov@chromium.org>
Reviewed-by: Victor Vianna <victorvianna@google.com>
Cr-Commit-Position: refs/heads/main@{#1026355}