Epic: Multi-document machine configuration and fully reactive Talos core

[smira]

These two issues seem to be intertwined, so we track them in a single Epic. At the same time there is no hard dependency between them.

High-Level Objectives

1. Machine configuration:
   1. Support additional configuration documents in the Talos machine configuration in addition to v1alpha1 document.
   2. Support different lifecycle of the documents - i.e. some documents might be removed, while other documents stay.
   3. Long-term: transition from v1alpha1 format to multi-doc format.
2. Reactive Talos core:
   1. Transform existing Talos sequencer and tasks into fully reactive controller-based implementation.
   2. Talos boot process should be fully async, acting on machine configuration changes.
   3. Any machine configuration change (with possibly some exceptions related to v1alpha1 format) should be applied without a reboot. The only exception is upgrade process which requires changing Linux kernel.

Task Breakdown

- [ ] #7225
- [ ] #7224
- [ ] https://github.com/siderolabs/talos/issues/7231
- [ ] https://github.com/siderolabs/talos/issues/7321
- [ ] https://github.com/siderolabs/talos/issues/8897