cmd/k8s-operator: migrate to tailscale-client-go-v2 (#19010)

This commit modifies the kubernetes operator to use the `tailscale-client-go-v2`
package instead of the internal tailscale client it was previously using. This
now gives us the ability to expand out custom resources and features as they
become available via the API module.

The tailnet reconciler has also been modified to manage clients as tailnets
are created and removed, providing each subsequent reconciler with a single
`ClientProvider` that obtains a tailscale client for the respective tailnet
by name, or the operator's default when presented with a blank string.

Fixes: https://github.com/tailscale/corp/issues/38418

Signed-off-by: David Bond <davidsbond93@gmail.com>

go.mod

@@ -94,7 +94,7 @@ require (
 	github.com/tailscale/goexpect v0.0.0-20210902213824-6e8c725cea41
 	github.com/tailscale/gokrazy-kernel v0.0.0-20240728225134-3d23beabda2e
 	github.com/tailscale/golang-x-crypto v0.0.0-20250404221719-a5573b049869
-	github.com/tailscale/hujson v0.0.0-20221223112325-20486734a56a
+	github.com/tailscale/hujson v0.0.0-20260302212456-ecc657c15afd
 	github.com/tailscale/mkctr v0.0.0-20260107121656-ea857e3e500b
 	github.com/tailscale/netlink v1.1.1-0.20240822203006-4d49adab4de7
 	github.com/tailscale/peercred v0.0.0-20250107143737-35a0c7bd7edc
@@ -115,7 +115,7 @@ require (
 	golang.org/x/exp v0.0.0-20250620022241-b7579e27df2b
 	golang.org/x/mod v0.31.0
 	golang.org/x/net v0.48.0
-	golang.org/x/oauth2 v0.33.0
+	golang.org/x/oauth2 v0.36.0
 	golang.org/x/sync v0.19.0
 	golang.org/x/sys v0.40.0
 	golang.org/x/term v0.38.0
@@ -136,6 +136,7 @@ require (
 	sigs.k8s.io/kind v0.30.0
 	sigs.k8s.io/yaml v1.6.0
 	software.sslmate.com/src/go-pkcs12 v0.4.0
+	tailscale.com/client/tailscale/v2 v2.9.0
 )
 
 require (