all-kube: create Tailscale Service for HA kube-apiserver ProxyGroup (#16572)

Adds a new reconciler for ProxyGroups of type kube-apiserver that will
provision a Tailscale Service for each replica to advertise. Adds two
new condition types to the ProxyGroup, TailscaleServiceValid and
TailscaleServiceConfigured, to post updates on the state of that
reconciler in a way that's consistent with the service-pg reconciler.
The created Tailscale Service name is configurable via a new ProxyGroup
field spec.kubeAPISserver.ServiceName, which expects a string of the
form "svc:<dns-label>".

Lots of supporting changes were needed to implement this in a way that's
consistent with other operator workflows, including:

* Pulled containerboot's ensureServicesUnadvertised and certManager into
  kube/ libraries to be shared with k8s-proxy. Use those in k8s-proxy to
  aid Service cert sharing between replicas and graceful Service shutdown.
* For certManager, add an initial wait to the cert loop to wait until
  the domain appears in the devices's netmap to avoid a guaranteed error
  on the first issue attempt when it's quick to start.
* Made several methods in ingress-for-pg.go and svc-for-pg.go into
  functions to share with the new reconciler
* Added a Resource struct to the owner refs stored in Tailscale Service
  annotations to be able to distinguish between Ingress- and ProxyGroup-
  based Services that need cleaning up in the Tailscale API.
* Added a ListVIPServices method to the internal tailscale client to aid
  cleaning up orphaned Services
* Support for reading config from a kube Secret, and partial support for
  config reloading, to prevent us having to force Pod restarts when
  config changes.
* Fixed up the zap logger so it's possible to set debug log level.

Updates #13358

Change-Id: Ia9607441157dd91fb9b6ecbc318eecbef446e116
Signed-off-by: Tom Proctor <tomhjp@users.noreply.github.com>

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