Add AlwaysAllowFledgeDeprecatedRenderURLReplacements flag.

Within a previous CL (https://chromium-review.googlesource.com/c/chromium/src/+/5412739), deprecatedRenderURLReplacements was disabled during cookie deprecation testing to avoid study interference. There is still some ongoing discussion on whether we really want this disabled or not. This new flag would provide the flexibility to collect data using deprecatedRenderURLReplacements alongside the study, if needed.

This change also contains a browser test to make sure it works as intended.

Bug: 333106234
Change-Id: Ic2bc4785a4149fdf49e8890311dff2a9dd966374
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5428147


Reviewed-by: David Bokan <bokan@chromium.org>
Reviewed-by: Russ Hamilton <behamilton@google.com>
Commit-Queue: Youssef Bourouphael <ybourouphael@google.com>
Cr-Commit-Position: refs/heads/main@{#1283527}