load_balancing: support header session affinity policy

[ColeBennett]

Adds support for the new header session affinity policy and its related session affinity attribute.

[github-actions]

changelog detected ✅

[ColeBennett]

Hi @jacobbednarz, this is ready for review

[jacobbednarz]

acceptance tests all passing

TF_ACC=1 go test ./internal/sdkv2provider -v -run "^TestAccCloudflareLoadBalancer_" -count 1 -timeout 120m -parallel 1
=== RUN   TestAccCloudflareLoadBalancer_Import
=== PAUSE TestAccCloudflareLoadBalancer_Import
=== RUN   TestAccCloudflareLoadBalancer_Basic
--- PASS: TestAccCloudflareLoadBalancer_Basic (5.34s)
=== RUN   TestAccCloudflareLoadBalancer_SessionAffinity
--- PASS: TestAccCloudflareLoadBalancer_SessionAffinity (4.84s)
=== RUN   TestAccCloudflareLoadBalancer_SessionAffinityIPCookie
--- PASS: TestAccCloudflareLoadBalancer_SessionAffinityIPCookie (5.16s)
=== RUN   TestAccCloudflareLoadBalancer_SessionAffinityHeader
--- PASS: TestAccCloudflareLoadBalancer_SessionAffinityHeader (5.57s)
=== RUN   TestAccCloudflareLoadBalancer_AdaptiveRouting
--- PASS: TestAccCloudflareLoadBalancer_AdaptiveRouting (5.16s)
=== RUN   TestAccCloudflareLoadBalancer_LocationStrategy
--- PASS: TestAccCloudflareLoadBalancer_LocationStrategy (5.17s)
=== RUN   TestAccCloudflareLoadBalancer_RandomSteering
--- PASS: TestAccCloudflareLoadBalancer_RandomSteering (8.56s)
=== RUN   TestAccCloudflareLoadBalancer_GeoBalanced
--- PASS: TestAccCloudflareLoadBalancer_GeoBalanced (5.26s)
=== RUN   TestAccCloudflareLoadBalancer_ProximityBalanced
--- PASS: TestAccCloudflareLoadBalancer_ProximityBalanced (5.06s)
=== RUN   TestAccCloudflareLoadBalancer_LeastOutstandingRequestsBalanced
--- PASS: TestAccCloudflareLoadBalancer_LeastOutstandingRequestsBalanced (5.05s)
=== RUN   TestAccCloudflareLoadBalancer_Rules
--- PASS: TestAccCloudflareLoadBalancer_Rules (5.31s)
=== RUN   TestAccCloudflareLoadBalancer_DuplicatePool
--- PASS: TestAccCloudflareLoadBalancer_DuplicatePool (2.25s)
=== RUN   TestAccCloudflareLoadBalancer_Update
--- PASS: TestAccCloudflareLoadBalancer_Update (8.79s)
=== RUN   TestAccCloudflareLoadBalancer_CreateAfterManualDestroy
--- PASS: TestAccCloudflareLoadBalancer_CreateAfterManualDestroy (8.55s)
=== CONT  TestAccCloudflareLoadBalancer_Import
--- PASS: TestAccCloudflareLoadBalancer_Import (6.04s)
PASS
ok  	github.com/cloudflare/terraform-provider-cloudflare/internal/sdkv2provider	86.666s

[github-actions]

This functionality has been released in v4.11.0 of the Terraform Cloudflare Provider.

Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template. Thank you!