Add "Brave Search Ads" line item and toggle to Manage Brave Ads

[Miyayes]

Description

Tasks

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1. Add "Brave Search Ads" line item and toggle to Manage Brave Ads section on brave://rewards. It should go above the Brave News Ads item.
2. If user is non-connected, then toggle is ON by default
3. If user is connected, then toggle this OFF by default
4. In connected case, show an extra tooltip that says: "You cannot earn BAT from Brave Search Ads yet, but you help support Brave by having them on. Brave Search Ads appear on Brave Search." "Brave Search" is hyperlinked to https://search.brave.com.
5. Update header that is sent to search.brave.com to map onto toggle value
6. In non-connected case, add tooltip that says: "Brave Search Ads appear on Brave Search". "Brave Search" is hyperlinked to https://search.brave.com.

Existing users:

1. Non-connected will have toggle ON
2. Connected will have toggle OFF

[aseren]

The X-Brave-Ads-Enabled header logic for iOS is implemented here
If we adding iOS support in the current ticket this code should also be changed.

cc @zenparsing @Miyayes

[aseren]

The X-Brave-Ads-Enabled header logic for iOS is implemented here If we adding iOS support in the current ticket this code should also be changed.

cc @zenparsing @Miyayes

Brave-Search-Ads support for iOS was added in the PR: brave/brave-core#23220