Integrate CookieControlsPageActionController with the browser

CookieControlsPageActionController, which manages the migrated cookie
controls page action path, is hooked up to the rest of the browser,
allowing it to take effect. This change consists of:
- Defining the browser action to trigger the page action
- Initializing the controller in TabFeatures
- Updating tests to use the new browser action to simulate invoking the page action
- Enabling the migration flag in fieldtrial_testing_config.json and adding it to the about://flags option.

Bug: 376283777
Change-Id: I4250c1c2d2193cbd02050a1591725a45d660ee6e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6956907
Commit-Queue: Kaan Alsan <alsan@chromium.org>
Reviewed-by: Dana Fried <dfried@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1526323}