Add DiffSuppressFunc to the linode_lke_cluster resource tier field

[lgarber-akamai]

📝 Description

This pull request adds a DiffSuppressFunc to the tier field of the linode_lke_cluster resource.

This prevents the recreation of clusters when managing a cluster without access to LKE tiers (e.g. using v4, cluster created before LKE-E, etc.).

NOTE: I'm not particularly happy with this solution so please let me know if you can think of any good alternative approaches.

Resolves #1945

✔️ How to Test

The following test steps assume you have pulled down this PR locally.

Integration Testing

make test-int PKG_NAME=lke TEST_ARGS="-run TestAccResourceLKECluster_tierNoAccess"

Manual Testing

1. In a terraform-provider-linode sandbox environment (e.g. dx-devenv), apply the following:

resource "linode_lke_cluster" "test" {
  label       = "tf-test-manual"
  region      = "us-mia"
  k8s_version = "1.33"
  tier = "standard"

  pool {
    type  = "g6-standard-1"
    count = 1
  }
}

2. Ensure the apply completes successfully.
3. Plan the configuration and ensure no changes are proposed.

[Copilot]

Pull Request Overview

This PR adds a DiffSuppressFunc to the tier field of the linode_lke_cluster resource to prevent unnecessary cluster recreation when managing clusters without access to LKE tier information (e.g., using v4 API or clusters created before LKE-E was available).

Key changes:

• Added diff suppression logic for the tier field when old value is empty and new value is "standard"
• Created test template and test case to validate the tier suppression behavior
• Extended template data structure to support tier field in tests

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
linode/lke/schema_resource.go	Added DiffSuppressFunc to suppress diffs when tier is empty and new value is "standard"
linode/lke/tmpl/tier_no_access.gotf	New test template for testing tier suppression with v4 API
linode/lke/tmpl/template.go	Added Tier field to TemplateData and TierNoAccess function
linode/lke/framework_resource_test.go	Added comprehensive test case for tier suppression functionality

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[lgarber-akamai]

Switching this to draft while I get confirmation about the approach for this issue.