Add Input Screen onboarding pixels

[joshliebe]

Task/Issue URL: https://app.asana.com/1/137249556945/project/488551667048375/task/1212082639780116?focus=true

Description

Adds the following pixels:

Fires during onboarding when the Search Experience view appears:
"m_preonboarding_choose_search_experience_impressions_unique"

Fires when the user selects the 'Search & Duck.ai' option during onboarding:
"m_preonboarding_aichat_selected"

Fires when the user selects the 'Search Only' option during onboarding:
“m_preonboarding_search_only_selected"

Steps to test this PR

Search & Duck.ai

• Fresh install, move the new onboarding step
• Verify m_preonboarding_choose_search_experience_impressions_unique is sent
• Select “Search & Duck.ai” and tap “Next"
• Verify that m_preonboarding_aichat_selected is sent

Search only

• Fresh install, move the new onboarding step
• Verify m_preonboarding_choose_search_experience_impressions_unique is sent
• Select “Search” and tap “Next"
• Verify that m_preonboarding_aichat_selected is sent

[joshliebe]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• Add Input Screen onboarding pixels #7196 👈 (View in Graphite)
• Add Input Screen onboarding step #7187 : 2 other dependent PRs (#7200 , #7239 )
• develop

This stack of pull requests is managed by Graphite. Learn more about stacking.

[github-actions]

Privacy Review task: https://app.asana.com/0/69071770703008/1212154554869999

[aitorvs]

LGTM