feat(snd): accept updateStrategy as an optional, ignored field

[bdchatham]

What

Re-adds the updateStrategy schema removed in #395 — now as an optional field the controller ignores (in-place remains the only rollout behavior). Schema-only; no consuming code returns.

Why

This is the migration-safe intermediate for retiring updateStrategy from the ~50 live SeiNodeDeployments. The field is a required → removed change with no optional step:

• the deployed CRD (d4c69a90) marks it required → purging it from manifests fails spec.updateStrategy: Required value
• the post-feat(snd): remove UpdateStrategy, make in-place rollout implicit (PLT-451 Phase 1) #395 CRD removes it → live objects carrying it fail field not declared in schema

There is no single schema under which the field is both present (on live objects) and absent (in purged manifests). An optional field is valid under both — so the eventual controller rollout's CRD accepts the existing objects with no pre-purge, dissolving the trap. (We hit the live form of this: a harbor manifest purge broke Flux and was reverted.)

Both the kubernetes-specialist and platform-engineer independently recommended this optional-intermediate over an atomic CRD-bump+purge (which races the apiserver's structural-schema propagation non-deterministically).

Scope

• +optional field + the UpdateStrategy/UpdateStrategyType types, regenerated CRD + deepcopy.
• Field is inert: nothing reads it; make manifests generate confirms it is not in spec.required.

Deferred (separate, unpressured)

Manifest cleanup (all cell manifests and seictl/nodedeployment/presets/*) and final field removal — tracked separately; no rollout pressure once the field is optional.

[cursor]

PR Summary

Low Risk
Schema-only CRD/API change with no controller logic; rollout behavior stays in-place.

Overview
Re-introduces spec.updateStrategy on SeiNodeDeployment as an optional, controller-ignored field so live clusters and GitOps manifests can coexist while the field is retired.

The API adds UpdateStrategy / UpdateStrategyType (InPlace only), documents that rollouts stay in-place, and regenerates CRD YAML and deepcopy. updateStrategy is not in spec.required, so manifests can omit it while existing objects that still set type: InPlace remain valid after the CRD update.

No reconciler or planner code reads this field; behavior is unchanged.

^{Reviewed by Cursor Bugbot for commit 10fdf1d. Bugbot is set up for automated code reviews on this repo. Configure here.}