fix(metricalarm): sync tags via TagResource/UntagResource on update

[mahasiva-amazon]

Fixes aws-controllers-k8s/community#2985

PutMetricAlarm silently ignores the Tags field when updating an existing alarm. As a result, tag changes made to a MetricAlarm CR were never propagated to AWS.

Additionally, DescribeAlarms does not return tags, so tags must be fetched separately via ListTagsForResource on every reconcile.

Solution

This PR fixes both issues:

1. Read path (sdk_read_many_post_set_output hook, committed in prior commit): Calls ListTagsForResource after every DescribeAlarms to populate Spec.Tags in the observed state, enabling accurate delta detection.

2. Write path (this commit): Adds a syncTags function in hooks.go that is called from sdkUpdate whenever Spec.Tags differs. It calls TagResource to add/update tags and UntagResource to remove tags no longer in the spec.

3. Short-circuit: A DifferentExcept("Spec.Tags") guard prevents an unnecessary PutMetricAlarm call when the delta is tags-only.

Files Changed

• generator.yaml — adds sdk_update_pre_build_request hook for MetricAlarm
• templates/hooks/metricalarm/sdk_update_pre_build_request.go.tpl — new hook template with tag sync and short-circuit logic
• pkg/resource/metric_alarm/hooks.go — new file with syncTags implementation
• pkg/resource/metric_alarm/sdk.go — regenerated with hook injected into sdkUpdate

Test plan

• Create MetricAlarm CR with env: test tag — alarm created in AWS with correct tag
• Patch CR to add team: platform tag — AWS alarm updated via TagResource
• Patch CR to remove team: platform tag — AWS alarm updated via UntagResource
• Tags-only update does not trigger PutMetricAlarm call
• ACK.ResourceSynced=True and Ready=True after each reconcile
• Builds cleanly with go build ./...
• All unit tests pass

🤖 Generated with Claude Code

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[ack-prow]

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