Make #brave-adblock-cookie-list-default enabled by default

[antonok-edm]

Resolves brave/brave-browser#29986

Submitter Checklist:

• I confirm that no security/privacy review is needed and no other type of reviews are needed, or that I have requested them
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally:
  • npm run test -- brave_browser_tests, npm run test -- brave_unit_tests wiki
  • npm run lint, npm run presubmit wiki, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Custom-Headers
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

See attached issue

[pes10k]

this is very good and i like it very much

[kjozwiak]

Verification PASSED on Win 11 x64 using the following build(s):

Brave | 1.59.76 Chromium: 116.0.5845.163 (Official Build) nightly (64-bit)
-- | --
Revision | 882a1d617108cea1c78439e27c5f19c46b276508
OS | Windows 11 Version 22H2 (Build 22621.2215)

Using the STR/Cases outlined via brave/brave-browser#29986 (comment), went through the following and ensured that brave://flags#brave-adblock-cookie-list-default enabled is being enabled by default on first launch.

• ensured that the Default for brave://flags#brave-adblock-cookie-list-default enabled is set as Enabled
• ensured that EasyList Cookies is enabled via brave://settings/shields/filters on first launch
• ensured that there's no cookie consent message appearing under https://www.digikey.com on first launch
• ensured that brave://flags#brave-adblock-cookie-list-default enabled is still enabled after restarting the browser
  • basically ensuring that once Griffin studies are being applied, #brave-adblock-cookie-list-default enabled is still enabled
  • ensured that EasyList Cookies is still enabled via brave://settings/shields/filters once Griffin studies are applied
• ensured that the cookie consent banner is appearing under https://www.digikey.com after disabling EasyList Cookies
  • disabled via brave://settings/shields/filters and ensured disabling/enabling worked as expected

Before Restarting (no Griffin studies applied)

Example	Example	Example	Example

After Restarting (Griffin studies being applied)

Example	Example

After disabling EasyList Cookies via brave://settings/shields/filters