[ads] Only collect, store and redeem essential conversion metadata for non-Rewards users

[tmancey]

Description

See https://github.com/brave/reviews/issues/1636 > 2.1

For non-Rewards users (see separate commits):

• [x] Only collect essential metadata for non-Rewards users
  • [x] Search result ad with no conversion url pattern should not be processed by the ads component
• [x] Only store clicked ad events for click-through conversions
• [x] Only redeem essential metadata for non-Rewards users
  • [x] Do not report viewed impressions
  • [x] Do not report clicks
  • [x] Do not report page lands/site visits
  • [x] Do not report httpResponseStatus in payload
  • [x] Do not report view-through conversions
  • [x] Report click-through conversions (Regular conversions)
  • [x] Do not report verifiable conversions [Already works as expected]
• [x] Remove non-essential ad events for non-Rewards users
  • [x] Discard legacy non-clicked ad events during database migration
  • [x] Ad events should be purged after 30 days*
  • [x] Purge Default/ads_service folder when resetting Brave Rewards [Already works as expected]
• [x] General code health

• For Rewards users we should continue to purge ad event history after 3 months due to frequency capping