Add Config v2 migration end-to-end coverage

[MrAlias]

Follow-up to #2679, blocked by #2682.

Migrate two existing Docker integration configurations and two existing Kubernetes integration configurations from v1 to v2. Run standalone OBI with each generated Config v2 file and verify the expected configuration is active.

Acceptance criteria:

• Reuse the four migration fixtures covered by Expose Config v2 validation and migration CLI #2679 where practical.
• Run the migration command for each selected v1 configuration.
• Start OBI through the standalone Config v2 runtime path introduced in Enable standalone Config v2 runtime loading #2682.
• Assert the selected workload behavior remains active, including the relevant selectors, exporters, and route configuration.

Receiver-specific Config v2 runtime coverage is handled separately in #2681.