Add NTP sponsored images frequency capping.

[aseren]

Now information about which SI should be rendered on NTP is requested from ads library.
NTP tries to render SI each 4th view. SI could be frequency capped. In this case NTP renders background wallpaper.

If Brave Ads are disabled, then frequency capping is not applied and SI is shown each 4th NTP view.

Resolves brave/brave-browser#14015

Submitter Checklist:

• I confirm that no security/privacy review is needed, or that I have requested one
• 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, npm run lint, 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:

Case 1

• Start browser with clean profile. Do not enable rewards. Enable rewards verbose logging.
• Check that NTP Sponsored images ads are shown on each 4th refresh of NTP.
• Enable rewards.
• Check that NTP SI ads become served by Ads Library. Each 4th NTP refresh requests NTP ad serving.
• If NTP ad wasn’t served then following message should appear in rewards log: New tab page ad not served
• Disable Brave Private Ads.
• Check that NTP Sponsored images ads are shown on each 4th refresh of NTP.

Case 2

• Start browser with clean profile. Enable rewards. Enable rewards verbose logging.
• NTP ad serving is first requested on second NTP refresh after browser start. After that it is requested each 4th NTP refresh. If NTP ad is served then it will be shown after 4 NTP refreshes.
• Check that NTP ad is served. There should be following message in rewards log: Served new tab page ad
• Check that if NTP ad is served, then it is shown on NTP after 4 refreshes. There should be following messages in rewards log: Viewed new tab page ad with placement id and Successfully logged new tab page ad viewed event.
• Check that subsequent attempts of NTP ad serving (at least during 5 minutes after success serving) are not successful and lead to New tab page ad not served message in rewards log.

[goodov]

++ DEPS

[simonhong]

ntp_background_images ++

[kylehickinson]

Looked at the wrong callback type, thanks, iOS++

[tmancey]

LGTM++ (added a couple nits)