v0.12.1

This release contains bugfixes and new metrics (along with some changes
to existing ones).

No breaking API changes.

Features:

- plugin: New migration-related metrics (#387):
  - autoscaling_plugin_migrations_created_total
  - autoscaling_plugin_migrations_deleted_total
  - autoscaling_plugin_migration_create_fails_total
  - autoscaling_plugin_migration_delete_fails_total
- plugin: Include node group in node resource metrics (#382)
- agent: agent->informant request metrics now include the endpoint (#380)

Fixes:

- Add vmscrape.yaml to release assets (#392)
- plugin: Fix spurious "updated scaling bounds" logs (#391)
  - Incidentally, this *also* entirely fixes our handling of scaling
    bounds changes.
- plugin: Migration handling reliability improvements (#387)
- informant: Fix parent process stall when child dies quickly (#389)
- agent: Fix NeonVM downscaling not showing up in metrics (#381)

No protocol changes.

No other changes.

Upgrade path from v0.12.0:

- No ordering requirements.