Retry transient Kubernetes API errors in chi kube driver Get calls

[aaron276h]

Fixes #2026.

Problem

Any Kubernetes API error during a CHI reconcile propagates up unchanged and the top-level handler aborts the entire reconcile (ErrCRUDAbort -> status: Aborted). Transient network errors (connection refused/reset, timeouts, apiserver 5xx) are treated the same as terminal ones (NotFound, Forbidden, ...).

On installations with hundreds of hosts, a reconcile issues tens of thousands of API calls over a long wall-clock window, so even a sub-second control-plane blip is nearly certain to land on one of them. We hit this repeatedly in production on a 387-host CHI:

FAILED to reconcile CR <ns>/<chi>, err: Get ".../configmaps/chi-<chi>-deploy-confd-data-a-87-0":
  dial tcp 10.x.0.1:443: connect: connection refused

with the abort landing at 385/387 hosts completed — nothing wrong in ClickHouse, one refused GET discarded the whole rollout. The 0.27 auto-recovery (reconcile.recovery.from.aborted.onPodReady) does not cover this case: all pods were already Ready, so no NotReady->Ready transition ever fires and the CR stays Aborted until an operator restart or spec edit.

Change

• New getWithRetry helper and isTransientAPIError classifier in pkg/controller/chi/kube.
• All Get calls in the chi kube drivers (ConfigMap, CR, PDB, Pod, PVC, Secret, Service, StatefulSet) retry transient errors with bounded exponential backoff: 5 attempts, 500ms -> 4s doubling (~7.5s worst-case budget).
• Transient = apiserver ServerTimeout/Timeout/TooManyRequests/InternalError/ServiceUnavailable/UnexpectedServerError, plus transport-level errors (ECONNREFUSED, ECONNRESET, EPIPE, ETIMEDOUT, EOF, net.Error).
• Terminal API errors (NotFound, AlreadyExists, Conflict, Forbidden, Unauthorized, BadRequest, Invalid, MethodNotSupported) and context cancellation return immediately, and exhausted retries return the last error unchanged — callers behave exactly as before for non-transient errors and sustained outages.
• Scope is deliberately reads-only: Get dominates the reconcile hot path (readiness polling) and is unconditionally safe to retry. Happy to extend to List (equally safe) if you'd like it in this PR.

Testing

• Unit tests for the classifier — including the exact url.Error -> net.OpError -> ECONNREFUSED nesting client-go produces — and for the retry loop (first-try success, retry-then-success, terminal short-circuit, retry exhaustion, context cancellation).

Notes for reviewers

• Backoff constants are package vars only so tests can shrink them; treated as read-only at runtime.
• Per-attempt retries log at V(2); giving up logs at V(1).