Layers added to a Function that has no layers in AWS are no longer ignored

[suprahh]

Issue #, if available: aws-controllers-k8s/community#3010

Description of changes

Adding layers to a Function that has no layers in AWS had no effect: the resource
was marked as synced and UpdateFunctionConfiguration was never called with the
Layers parameter.

sdkFind() builds the latest resource from a deep copy of the desired one. When
GetFunction returns no layer, the else branch only cleared
Status.LayerStatuses and left Spec.Layers holding the desired value inherited
from that deep copy. desired and latest were then identical, so
delta.DifferentAt("Spec.Layers") never became true and the guard in
updateFunctionConfiguration skipped the field.

Clearing Spec.Layers as well makes the latest resource reflect the actual state
in AWS, so the delta is computed. The code lives in the
sdk_read_one_post_set_output hook template and is injected into
pkg/resource/function/sdk.go, so both files carry the same change. Nothing was
regenerated, so ack-generate-metadata.yaml is untouched (same approach as #174).

Why the existing e2e test did not catch it

test_function_layers creates the function with layers already attached and only
replaces them, so the else branch is never exercised. This adds
test_function_add_layers_to_function_without_layers, which starts from a
function without layers and then adds them.

Verification

Run against a real AWS account in us-west-2. Before the fix the new test fails
with KeyError: 'Layers'; after the fix it passes. test_function_layers still
passes, so replacing existing layers is unaffected.

Also reproduced the original adoption scenario by hand: a Function adopted with no
layers in AWS and patched with spec.layers reported ACK.ResourceSynced=True
with an empty status.layerStatuses while AWS still had Layers: null. Running
the fixed controller against the same CR, without touching it, attached the layers.

By submitting this pull request, I confirm that my contribution is made under the
terms of the Apache 2.0 license.

[ack-prow]

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[ack-prow]

Hi @suprahh. Thanks for your PR.

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[bugbuilder]

Cool to have it in the next release! Kudos @suprahh