[ads] Search result attribution on iOS

[aseren]

Resolves brave/brave-browser#33469

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 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/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

Test case 1

• Enable ShouldAlwaysRunBraveAdsService feature
• Enable ShouldSupportSearchResultAds feature
• Enable ShouldAlwaysTriggerBraveSearchResultAdEvents feature
• Make sure that Brave Ads service is started
• Trigger search result ad on search.brave.com
• Check that search result ad served event was triggered in ads service. There should be [ads] Served search result ad with placement id log message
• Check that search result ad viewed event was triggered in ads service. There should be [ads] Viewed search result ad with placement id log message
• Click an ad and stay in the opened page for some time
• Check that search result ad clicked event was triggered in ads service. There should be [ads] Clicked search result ad with placement id log message
• Check that landed event was triggered in ads service. There should be [ads] Landed on page for <URL> log message
• Do an ad conversion. Conversion URL can be found in ad metadata
• Check that conversion event was triggered in ads service. There should be [ads] Successfully added click conversion for search_result_ad log message

Test case 2

• Enable ShouldAlwaysRunBraveAdsService feature
• Disable ShouldSupportSearchResultAds feature
• Enable ShouldAlwaysTriggerBraveSearchResultAdEvents feature
• Make sure that Brave Ads service is started
• Trigger search result ad on search.brave.com
• Check that search result ad served event wasn't triggered.
• Check that search result ad viewed event wasn't triggered.
• Check that search result ad clicked event wasn't triggered.

Test case 3

• Enable ShouldSupportSearchResultAds feature
• Enable ShouldAlwaysRunBraveAdsService feature
• Enable ShouldAlwaysTriggerBraveSearchResultAdEvents feature
• Make sure that Brave Ads service is started
• Join Brave Rewards
• Make sure that we cannot get ad on search.brave.com
• Check that search result ad served event wasn't triggered.
• Check that search result ad viewed event wasn't triggered.

[tmancey]

LGTM (Please see comment)

[tmancey]

LGTM++

[tmancey]

LGTM++ (See comment)