Migrate source_code_pushes to snowplow

What does this MR do and why?

Related to #362281 (closed)

We're moving counters from Service Ping to Snowplow. source_code_pushes is one of the counters that we want to move.

Screenshots or screen recordings

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How to set up and validate locally

1. Enable snowplow micro
2. Run sidekiq with snowplow micro enabled [ SNOWPLOW_MICRO_ENABLE=true bundle exec sidekiq]
3. Push code to a repository
4. Check if a new event with source_code_pushes action has been registered at localhost:9090/micro/good

MR acceptance checklist

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