cmd/k8s-proxy: importing feature/condregister on cmd/k8s-proxy (#17383)

https://github.com/tailscale/tailscale/pull/17346 moved the kube and aws
arn store initializations to feature/condregister, under the assumption
that anything using it would use kubestore.New. Unfortunately,
cmd/k8s-proxy makes use of store.New, which compares the `<prefix>:`
supplied in the provided `path string` argument against known stores. If
it doesn't find it, it fallsback to using a FileStore.

Since cmd/k8s-proxy uses store.New to try and initialize a kube store in
some cases (without importing feature/condregister), it silently creates
a FileStore and that leads to misleading errors further along in
execution.

This fixes this issue by importing condregister, and successfully
initializes a kube store.

Updates #12614

Signed-off-by: chaosinthecrd <tom@tmlabs.co.uk>

cmd/k8s-proxy/k8s-proxy.go

@@ -31,6 +31,7 @@ import (
 	"k8s.io/utils/strings/slices"
 	"tailscale.com/client/local"
 	"tailscale.com/cmd/k8s-proxy/internal/config"
+	_ "tailscale.com/feature/condregister"
 	"tailscale.com/hostinfo"
 	"tailscale.com/ipn"
 	"tailscale.com/ipn/store"