TPT-4206: Integration tests for NB Front-End IP & 40Gbps

[mawilk90]

📝 Description

Integration tests for NodeBalancer Front-End IP in VPC and 40Gbps NodeBalancer-MTC

NOTE:
There is no valid region on DevCloud to create nodebalancers of type=premium_40gb so one test will fail. I decided to do not add 'skipif' dependent on the env, because we usually do not execute tests on DevCloud

✔️ How to Test

make test-int TEST_ARGS="-run TestNodeBalancer_Create_With"

[mawilk90]

There are two tests that check API error message in case of invalid nodebalancer's request body (similarly as it was in python SDK). I'm not sure what is the correct approach here so decided to leave them but comment them out (since they are expected to fail there is no fixtures for them at all)

[Copilot]

Pull request overview

Adds/updates integration tests to validate NodeBalancer behavior when using VPC front-end IPs (premium) and the premium_40gb NodeBalancer type, along with supporting test utilities and recorded fixtures.

Changes:

• Extend NodeBalancer integration tests to cover: backend-VPC-only, frontend-VPC-only (premium), frontend+backend in different VPCs, and premium_40gb.
• Update VPC creation helpers to select regions using linodego.Capability* constants (and include NodeBalancer capability).
• Add a generic getIntersection helper and new VCR fixtures for the added test cases.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
test/integration/vpc_subnet_test.go	Adjusts region capability filtering for VPC creation helpers used by integration tests.
test/integration/util_test.go	Adds a generic slice intersection helper used for region selection.
test/integration/nodebalancers_test.go	Adds new NodeBalancer/VPC integration tests and setup helpers, plus region selection logic.
test/integration/fixtures/TestNodeBalancer_Create_WithBackendVPCOnly.yaml	New recorded fixture for backend-VPC-only NodeBalancer creation.
test/integration/fixtures/TestNodeBalancer_Create_WithFrontendVPCOnly.yaml	New recorded fixture for frontend-VPC-only (premium) NodeBalancer creation.
test/integration/fixtures/TestNodeBalancer_Create_WithFrontendAndBackendInDifferentVPCs.yaml	New recorded fixture for frontend+backend in different VPCs.
test/integration/fixtures/TestNodeBalancer_Create_WithPremium40gbType.yaml	New recorded fixture for premium_40gb NodeBalancer creation.

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