add load_id to _dlt_versions table

[rudolfix]

Background
We want the users to be able to link the loads in _dlt_loads to _dlt_versions to identify which load updated the schema without enabling the trace (https://dlthub.com/docs/running-in-production/running#inspect-and-save-the-load-info-and-trace).

Tasks

1. • insert load_id into the _dlt_versions, see SqlJobClientBase
2. • you need to change the _dlt_versions schema definition (schema/utils.py) - make sure it is NULLABLE so old dlt installations can migrate
3. • we need to increase schema engine version and write migration that will add the column to existing schema (schema/utils.py)

Tests

1. Extend existing tests for updating schema and make sure the load_id is stored (test_job_client.py)
2. Test the schema migration: mock the schema to not have this column, load data, then load the schema again and load the data again to make sure the schema was added