v0.23.0

Substantial release with many bugfixes and quality-of-life improvements.
Notable inclusions: SSH support for VMs, opt-in higher log throughput,
tech debt resolution inside the scheduler.

Features:

- neonvm: Clock synchronization using kvm_ptp (#732)
- neonvm: Enable SSH access into the VMs (#726)
- neonvm-controller: Expose default set of metrics (#739)
- neonvm-controller: Custom reconciler metrics (#757)

No breaking changes (kind of; see "Protocol changes").

Protocol changes:

- agent,plugin: Refer to memory quantities in bytes, not memory slots (#653)
- agent: Send compute unit in requests to plugin (#744)

Fixes:

- neonvm-runner: Use the right file extension for ISO images (#735)
- agent: Add small random amount to plugin requset tick (#745)
- agent: Sleep for random delay before first metrics request (#746)
- neonvm-runner: Pass logs through virtio-serial (#724)

No other changes.

Upgrade path from v0.22.0:

- The neonvm deployment must be updated BEFORE making use of the new
  vm-builder version, else ssh access and clock synchronization will not
  work.
- The new `spec.enableSSH` field on VMs is ignored by previous versions
  of the scheduler and autoscaler-agents; no ordering requirement there.
- The scheduler MUST be updated before autoscaler-agents, due to the
  protocol changes between them.