Disables Brave suggested sites by default

[ryanml]

Fixes brave/brave-browser#10131

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Verified that these changes build without errors on
  • Android
  • iOS
  • Linux
  • macOS
  • Windows
• Verified that these changes pass automated tests (unit, browser, security tests) on
  • iOS
  • Linux
  • macOS
  • Windows
• Verified that all lint errors/warnings are resolved (npm run lint)
• Ran git rebase master (if needed).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.
• Request a security/privacy review as needed.
• Add appropriate QA labels (QA/Yes or QA/No) to include the closed issue in milestone
• Public documentation has been updated as necessary. 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-issues-with-tracking-protection
  • https://github.com/brave/brave-browser/wiki/QA-Guide

Test Plan:

Reviewer Checklist:

• New files have MPL-2.0 license header.
• Request a security/privacy review as needed.
• Adequate test coverage exists to prevent regressions
• Verify test plan is specified in PR before merging to source

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.

[emerick]

LGTM

[ryanml]

Tests pass, builds generated, failure unrelated

[srirambv]

Verification passed on

Brave	1.12.5 Chromium: 83.0.4103.61 (Official Build) nightly (64-bit)
Revision	94f915a8d7c408b09cc7352161ad592299f384d2-refs/branch-heads/4103@{#561}
OS	Linux

• Verified on clean install Brave suggested sites setting is disabled by default
• Verified with setting off, there are no Brave suggested site suggestion show up for various tokens and partners links
• Verified upgrading from 1.11.27 to 1.12.5 setting is turned off automatically
• Verified disabling the setting in 1.11.27 and then upgrading to 1.12.5 retains the setting
• Verified on upgrade with setting disabled, there are no Brave suggested sites suggestions show up for various tokens and partner links