Added support for tier in lkeversion and lkeversions datasources

[ezilber-akamai]

📝 Description

Added the lkeversion datasource. Also added support for the tier field in the lkeversions datasource.

The lkeversion datasource can be used to call both GET /v4beta/lke/versions/<versionID> and GET /v4beta/lke/versions/<tier>/<versionID> endpoints.

The lkeversions datasource can be used to call both GET /v4beta/lke/versions/<tier> and GET /v4beta/lke/versions endpoints.

✔️ How to Test

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

Unit Tests

make test-unit

Integration Tests

make test-int PKG_NAME="lkeversion" TEST_CASE="TestAccDataSourceLinodeLkeVersion"
make test-int PKG_NAME="lkeversions" TEST_CASE="TestAccDataSourceLinodeLkeVersions"

Manual Tests

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

1. Using a terraform-provider-linode sandbox environment (e.g. dx-devenv), apply the following configuration (make sure to use v4beta):

data "linode_lke_versions" "versions_no_tier" {}

output "lke_versions_no_tier" {
  value = data.linode_lke_versions.versions_no_tier
}

data "linode_lke_versions" "versions_tier" {
    tier = "enterprise"
}

output "lke_versions_tier" {
  value = data.linode_lke_versions.versions_tier
}

data "linode_lke_version" "version_no_tier" {
    id = "1.31"
}

output "lke_version_no_tier" {
  value = data.linode_lke_version.version_no_tier
}

data "linode_lke_version" "version_tier" {
    id = "v1.31.1+lke1"
    tier = "enterprise"
}

output "lke_version_tier" {
  value = data.linode_lke_version.version_tier
}

2. Ensure the output is accurate.

[ezilber-akamai]

I was not able to find a way to entirely omit the tier fields from the state when the user does not provide it. Instead, it shows up in the state with a value of null. Any ideas on how to improve this?

[zliang-akamai]

Can we use statecheck for newly implemented tests?
https://developer.hashicorp.com/terraform/plugin/testing/acceptance-tests/state-checks/resource