[Digital Goods API] Enable DGAPI by default.

This patch enabled DGAPI 2.0 by default, as the "intent to ship" was
approved on blink-dev@chromium.org. There are no code changes from the
current origin trial to what we intend to ship to stable. Therefore,
there is no new tracking bug or launch bug being filed.

Intent to ship:
https://groups.google.com/a/chromium.org/g/blink-dev/c/2pjQ3O2GzDA/m/T2AC1LR3BQAJ
Explainer: https://github.com/WICG/digital-goods/blob/main/explainer.md
Spec: https://wicg.github.io/digital-goods/

Bug: 1248319, 1250123
Change-Id: I8783b93a8d5594e2ea519e5a836b717892a39896
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3439111
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Rouslan Solomakhin <rouslan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#968088}