Add additional Rewards metrics

[DJAndries]

Resolves brave/brave-browser#38567

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:

Start with fresh profile, ensure no metrics are present. Enable Rewards.

For Brave.Rewards.AdTypesEnabled.2:

0. Ensure initial metric value is 7.
1. Toggle some ad types, ensure metric value is correct.

For Brave.Rewards.SearchResultAdsOptin

0. Turn off & turn on search ads. Ensure metric does not exist
1. Turn off search ads and connect a payout account. Ensure metric does not exist
2. Turn on search ads, ensure metric exists with value 1.

For Brave.Rewards.AdsHistoryView:

View ads history, ensure metric has value 1.

[zenparsing]

This is fine for now, but if this callback grows any more complex we'll probably want to split it into different callbacks or have this one accept an options struct or an enum value.

[iefremov]

don't we have tests for those? can we add one?