Document the dolt_ci_workflow_* system tables

Fourteen system tables related to Dolt CI workflows are registered in the canonical system-table registry at [`doltdb/system_table.go`](https://github.com/dolthub/dolt/blob/main/go/libraries/doltcore/doltdb/system_table.go) but have no documentation in [`reference/sql/version-control/dolt-system-tables.md`](https://github.com/dolthub/docs-2/blob/main/site/dolt/src/content/reference/sql/version-control/dolt-system-tables.md):

- `dolt_ci_workflows`
- `dolt_ci_workflow_events`
- `dolt_ci_workflow_event_triggers`
- `dolt_ci_workflow_event_trigger_branches`
- `dolt_ci_workflow_event_trigger_activities`
- `dolt_ci_workflow_jobs`
- `dolt_ci_workflow_steps`
- `dolt_ci_workflow_saved_query_steps`
- `dolt_ci_workflow_saved_query_step_expected_row_column_results`
- `dolt_ci_workflow_dolt_test_steps`
- `dolt_ci_workflow_dolt_test_step_groups`
- `dolt_ci_workflow_dolt_test_step_tests`

This is a related family of tables, so probably wants either a new sub-section in `dolt-system-tables.md` ("CI workflow tables") or a dedicated page under `products/dolthub/continuous-integration/`. Each table needs a schema + brief description. Add the resulting anchors to `sql-extensions.md` once documented.

Surfaced during the source-vs-docs cross-check for #43 (see #64).