chrome://flags should enable OriginTrialFeedback

In order to ensure that developers are testing the version of DBSC most
likely to ship, we want to make sure that OriginTrialFeedback is enabled
by the chrome://flags entry. This is easiest if its a FeatureParam
instead of an independent Feature.

In order to make sure that we don't carry across sessions with
incompatible semantics, changing the flag value also changes the session
schema version.

Fixed: 443948853
Change-Id: Ia4175128af4a1d05cf301c55103687c4b367641f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6986108
Commit-Queue: Daniel Rubery <drubery@chromium.org>
Reviewed-by: Vladimir Levin <vmpstr@chromium.org>
Reviewed-by: thefrog <thefrog@chromium.org>
Reviewed-by: Nidhi Jaju <nidhijaju@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1522274}