TPT-3925: Use omitzero for ACLP alerts to support empty lists

[yec-akamai]

📝 Description

Use omitzero for alerts to make sure it explicitly pass an empty list instead of null.

Address terraform test issue: linode/terraform-provider-linode#2259

✔️ How to Test

make test-unit

[Copilot]

Pull request overview

This PR updates the Linode instance “ACLP alerts” structures to use pointer-to-slice fields so callers can explicitly send empty alert lists ([]) instead of having the field omitted (nil) during JSON marshaling, addressing downstream Terraform test expectations.

Changes:

• Change InstanceAlert and InstanceACLPAlertsOptions alert list fields from []int to *[]int.
• Update unit tests to handle pointer alert lists when reading and constructing request options.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 10 comments.

File	Description
instances.go	Switches alert list fields to *[]int to distinguish omitted vs explicitly empty arrays in JSON.
test/unit/instance_test.go	Adjusts tests to dereference alert list pointers and updates request option construction accordingly.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[mgwoj]

PR title does not match the final changes. Also the changes in the code are not aligned with the changes in the tests.

[yec-akamai]

PR title does not match the final changes. Also the changes in the code are not aligned with the changes in the tests.

Updated the PR title. There is not much to change in the test case since we avoid to make breaking changes. Already verfied the omitzero works as expected across terraform.

[mgwoj]

Which tests is showing that this change with omitzero works?