Migrate i_code_review_create_mr to total counts

Problem

The metrics i_code_review_create_mr_monthly and i_code_review_create_mr_weekly are supposed to count the total number of merge requests created in a 7d/28d time frame.

Until #411264 (closed) we actually did not support time-based total counts, but only counts based on a uniqueness trait (e.g. user_id). To work around this restriction the event i_code_review_create_mr is actually using a value that's always unique for this event, the merge_request_id (see code). This is misleading, a suboptimal usage of RedisHLL, and makes the metrics impossible to automatically mirror into Snowplow.

Desired Outcome

Both the monthly and weekly version of i_code_review_create_mr_monthly:

• are migrated towards using a total counter with the same time frame as before
• use the same key as before
• just continue the count from the RedisHLL metric, since we want to keep the history for SM customers

Potential Solution

TBD

Further Actions

Inform @mdrussell that the metric has been migrated as soon as it's done.