feat: Database forward compatibility: make owner field optional

[sokoliva]

Description

Old version is not able to write in databases which are 1.0 compatible because the new owner field is mandatory. This change makes the owner field optional to maintain forward compatibility.

Tested

Before change (owner field mandatory)

I created a database with tables tasks and push_notification_configs using 1.0 spec. I then tested it against 0.3 spec by trying to write in it. It failed returning an error: NOT NULL constraint failed: tasks.owner.

Also, I created a database with 0.3 spec Task and PushNotificationConfigs entries but then made it 1.0 compatible via migration CLI command uv run a2a-db. Reading such data using 0.3 spec worked, but writing failed for the same reason as before.

After change (owner field optional)

I repeated the testing from before. Now writing in 1.0 compatible databases worked.

Notes

Writing in database which was created using 1.0 spec without running the migration a2a-db CLI command, created entries which have owner=NULL values, contrary to databases that underwent the migration using a2a-db which have owner field populated with the default value. In my case with legacy_v03_no_user_info since I didn't use the --add_columns_owner_last_updated-default-owner flag to pass my own custom default value.

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Fixes #811 🦕