add user_id and session_number to session tables

[dgitis]

Description & motivation

The way that our tables are currently architected, we can't get a daily user count and returning users without querying the client and user tables that aren't partitioned.

In order to let people get these metrics, this PR adds user_id and session_number to the fct_ga4__sessions_daily and fct_ga4__sessions tables.

This will allow users to get new and returning users by running queries like count(distinct case when session_number = 1 then ifnull(user_id, client_key) else null end) as new_users or count( distinct ifnull(user_id, client_key)) as users against the sessions table and not query all data for all time.

Checklist

• [y ] I have verified that these changes work locally
• [n/a ] I have updated the README.md (if applicable)
• [ n/a ] I have added tests & descriptions to my models (and macros if applicable)
• [ y] I have run dbt test and python -m pytest . to validate existing tests

[adamribaudo-velir]

In the case of a multi-day session, user_id could be null on day 1 and have a value on day 2. This would result in 2 rows with the same session_key. Should we take the max(user_id) here as well?

[adamribaudo-velir]

@dgitis take a look at my updates and feel free to merge if they look good.

[dgitis]

I seem to have failed to commit changes that added max(user_id) to both models and that addressed the column name error. My apologies.