[Telemetry] Add default browser to baseline ping

[bbinto]

Understand how many users selected Fenix as their default browser

• As a product owner, I want to know how many users selected Fenix as their default browser, so I can track success of the product

What questions will you answer with this data?

• How many people use Fenix as their default Browser, if this number grows, our main MAU and DAU KPIs will increase

Why does Mozilla need to answer these questions? Are there benefits for users? Do we need this information to address product or business requirements?

• An increase/decrease will indicate happiness, stickiness and usefulness of the browser

What probes

• maybe in core ping as part of browser_default: yes/no?

Acceptance Criteria (Added by PM)

• Pings can be queried via re:dash
• We are sending telemetry events for the actions listed in the requirements
• We have documented the telemetry
• We have asked a data steward to review the telemetry

┆Issue is synchronized with this Jira Task

[georgf]

What probes

* maybe in core ping as part of browser_default: yes/no?

As a product metric, i would put this as a boolean metric into metrics.yaml.
This means it will be sent ~daily through the metrics ping, which should be sufficient for the requirements here.

If analysis in Amplitude is needed, adding an event instrumentation would be needed.