further prep for integration tests

[awprice]

Further prep for integration tests

Follow-up to #144. Two production changes and their unit tests.

Changes

pkg/k8s — use merge patch for node annotations and labels

AddAnnotationToNode and AddLabelToNode previously used a JSON Patch
"add" operation. This fails at the apiserver when the node's
metadata.annotations / metadata.labels map is nil — something that
happens in envtest (no kubelet to initialise the map) and occasionally in
real clusters before a kubelet has written its own annotations.

Both functions now use a strategic merge patch via the new MergePatchNode
helper, which the apiserver handles correctly regardless of whether the map
exists. Behaviour in normal clusters is identical.

8 unit tests added in pkg/k8s/node_test.go, including an explicit
nil-annotations case that would have failed before this change.

pkg/manager — extract controller wiring into Run

cmd/manager/main.go used to inline scheme registration and all three
reconciler registrations. The integration test world package had to
duplicate that wiring, meaning any future change to controller setup could
silently diverge between production and tests.

pkg/manager.Run(ctx, mgr, deps) is now the single place that registers
the cyclops scheme, metrics, and all three controllers.
cmd/manager/main.go and the integration test suite both call it.

2 unit tests added in pkg/manager/manager_test.go.

[mwhittington21]

LGTM