[WIP] [V2] Emit action events as Kubernetes Events

[jeffoodchain]

Tracking issue

Closes #7829
Related to #7903

Why are the changes needed?

Flyte 1 pushed each execution event to a message broker. Flyte 2 has no such path, so
systems outside Flyte (lineage, alerting, cost accounting) cannot react to action events.

The design in #7903 solves this without a broker client in Flyte. The executor emits each
action event as a k8s Event on the TaskAction. An operator deploys a third-party
exporter (for example resmoio/kubernetes-event-exporter) and routes the events to Kafka, Loki, or a webhook.

What changes were proposed in this pull request?

Design Doc: #7903

This PR is still work in progress, and will be updated frequently.

Done:

• truncateUTF8: cut a note to the 1024-byte apiserver limit and keep valid UTF-8. (in doc, it is truncateRunes)
• Export actionsk8s.IsTerminalPhase so the executor can reuse it.
• EventLevel (off, terminal, info, debug) and eventLevelOf, which classifies an action event. A system retry is a QUEUED event in the reserved version range.
• buildActionEventK8s: build an events.k8s.io/v1 Event from an ActionEvent.

TODOs:

• Set ReportingInstance on the reconciler.
• Limit the size of flyte.org/info. The apiserver caps all annotations of one object at 256 KiB.
• Add parent-action-name and task-type annotations. Remove the unused launch-plan and principal keys (TaskActionSpec has neither).
• Decide the run annotation key: flyte.org/run-name or the existing label key flyte.org/run.
• Unit tests for the emit path (fake client and fake recorder).
• Verify on a devbox: the apiserver accepts the event, and the exporter can match and template it.
• e2e tests for different consumer
• Document the exporter setup and the delivery guarantees: events live for 1h, delivery is at-least-once, consumers dedupe on (action-name, attempt, phase, version).

How was this patch tested?

Unit tests in executor/pkg/controller/k8s_event_test.go:

• TestTruncateUTF8: ASCII cases, a cut inside a multi-byte rune, invalid bytes.
• TestBuildActionEventK8s: fields the apiserver validates, error annotations with and
  without ErrorInfo, and flyte.org/info decodes back to the original event.
• TestEventLevelOf, TestEventType, TestEventReason, TestHumanSummary.

Not tested yet: no apiserver has accepted one of these events. That is the devbox item above.

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Related PRs

#7903