378 refactor valid date away from created_at

[acatchpole]

Card: bcgov/cas-reporting#378

Changes

• Activity service: GET changed to use reporting_year_id instead of created_at
• activity_save_service: POST changed to use reporting_year_id instead of created_at
• updated relevant tests to use reporting_year_id and hardcoded in a valid reporting_year, otherwise the model bakery try using the year -7643453423 (because the reporting_year is an int field, and not a date field)
• Updated name of supporting function (get_report_valid_year_from_version_id -> get_report_valid_date_...) to more accurately reflect the functions purpose.

Note:

The ticket included removing facility_id after the refactor since it would no longer be used. Work in (this)[https://github.com/bcgov/cas-reporting/issues/522] ticket likely mean it is still needed.