Add final telemetry for wallpaper v2

[onemahon]

Update telemetry with metrics required for wallpapers V2 as defined in #26908

Metrics should include:

• adding a source extra to wallpaper selections from the wallpaper settings page (see https://github.com/mozilla-mobile/fenix/pull/26893)
• clicks on link to learn more, including which wallpaper collection and link are being clicked

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