fix: retry reconcile on transient errors during reconcile (envoyproxy#6299)

* fix: add isTransientError helper to classify retryable errors

Introduces isTransientError to detect transient Kubernetes errors and
enable proper reconciliation retries.

Signed-off-by: Patryk Rostkowski <[email protected]>

handle errors from processing BackendRefs

Signed-off-by: Huabing (Robin) Zhao <[email protected]>

handle errors from processing ConfigMap

Signed-off-by: Huabing (Robin) Zhao <[email protected]>

* skip invalid GatewayClass

Signed-off-by: Huabing (Robin) Zhao <[email protected]>

* address comment

Signed-off-by: Huabing (Robin) Zhao <[email protected]>

* handle all transient errors

Signed-off-by: Huabing (Robin) Zhao <[email protected]>

* don't skip failed GCs

Signed-off-by: Huabing (Robin) Zhao <[email protected]>

---------

Signed-off-by: Patryk Rostkowski <[email protected]>
Signed-off-by: Huabing (Robin) Zhao <[email protected]>
Co-authored-by: Huabing (Robin) Zhao <[email protected]>

Author: patrostkowski