add active period start/end timestamp columns and cleanup yaml

[lauriemerrell]

Description

Describe your changes and why you're making them. Please include the context, motivation, and relevant dependencies.

• Was adding active_period_start_ts in GTFS RT date, time, and trip labeling updates #2489 and realized it should just go on the main fct table
• Cleaning up some YAML I missed before in Refactor unnesting for service alerts #2583

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation

How has this been tested?

Include commands/logs/screenshots as relevant.

Full refreshed fct_service_alerts_messages_unnested and confirmed new columns appear and seem reasonable. New test passes and I looked at the executed SQL and confirmed that __rt_sampled__ is compiling as expected.

Post-merge follow-ups

Document any actions that must be taken post-merge to deploy or otherwise implement the changes in this PR (for example, running a full refresh of some incremental model in dbt). If these actions will take more than a few hours after the merge or if they will be completed by someone other than the PR author, please create a dedicated follow-up issue and link it here to track resolution.

• No action required (well, I have to rebase GTFS RT date, time, and trip labeling updates #2489)
• Actions required (specified below)

[github-actions]

Warehouse report 📦

New models 🌱

mart.gtfs.fct_service_alerts_messages_unnested
intermediate.gtfs.int_gtfs_rt__service_alerts_fully_unnested

Changed models 🔀

mart.transit_database.dim_organizations
mart.payments.elavon_littlepay__daily_history_transactions_deposits_billing
mart.gtfs.fct_daily_service_alerts
mart.gtfs.fct_service_alerts_trip_summaries