Promote `PortPolicyNone` Feature Gate from Beta to Stable

[markmandel]

What does this feature do?

PortPolicyNone enables a portPolicy: None option on GameServer port definitions. When set:

• Agones performs no dynamic host port allocation
• The hostPort field is ignored
• status.ports[].port returns the containerPort value rather than a dynamically assigned host port
• Useful for workloads that rely on container networking directly (e.g., service mesh, CNI plugins)

Current state: Beta (enabled by default since 1.49.0)

Acceptance Criteria / Tasks

• Manual audit: Before starting, grep the repo for FeaturePortPolicyNone and PortPolicyNone to confirm all usage sites — the list below may not be exhaustive
• Remove the FeaturePortPolicyNone feature gate check from pkg/apis/agones/v1/gameserver.go — fold the gated logic to always-true (unconditionally allow portPolicy: None and return containerPort in status)
• Remove the GKE Autopilot feature gate check for PortPolicyNone in pkg/cloudproduct/gke/gke.go
• Move FeaturePortPolicyNone from // Beta features to // Stable features in pkg/util/runtime/features.go (keep it in featureDefaults as true so old feature-gate strings don't fail to parse)
• Move PortPolicyNone from Beta to Stable section in install/helm/agones/defaultfeaturegates.yaml
• Remove PortPolicyNone from BETA_FEATURE_GATES in build/Makefile
• Remove PortPolicyNone=false from the inverted e2e-runner config in cloudbuild.yaml
• Update site/content/en/docs/Guides/feature-stages.md — move row from Beta table to Stable table
• Update test/upgrade/versionMap.yaml — add entry showing PortPolicyNone moves to stable gates in this release
• Clean up any unit/e2e tests that conditionally skip or toggle FeaturePortPolicyNone (e.g., TestGameServerPortPolicyNone in test/e2e/gameserver_test.go, tests in pkg/apis/agones/v1/gameserver_test.go)

Files to change

File	Change
pkg/util/runtime/features.go	Move FeaturePortPolicyNone const + default to Stable section
pkg/apis/agones/v1/gameserver.go	Remove FeatureEnabled(FeaturePortPolicyNone) guards; fold logic unconditionally
pkg/cloudproduct/gke/gke.go	Remove FeaturePortPolicyNone check
pkg/apis/agones/v1/gameserver_test.go	Remove feature-gate-disabled test cases
pkg/cloudproduct/gke/gke_test.go	Remove feature-gate-disabled test cases
test/e2e/gameserver_test.go	Remove t.Skip guard on TestGameServerPortPolicyNone
install/helm/agones/defaultfeaturegates.yaml	Move to Stable section
build/Makefile	Remove from BETA_FEATURE_GATES
cloudbuild.yaml	Remove PortPolicyNone=false from inverted e2e config
site/content/en/docs/Guides/feature-stages.md	Move row to Stable table
test/upgrade/versionMap.yaml	Add stable entry for this release

Verification

• make lint test-go passes with no skipped PortPolicyNone-gated test cases
• E2E test TestGameServerPortPolicyNone runs without any feature-gate skip
• A GameServer with portPolicy: None can be created without needing to set the feature gate
• Setting PortPolicyNone=true or PortPolicyNone=false in the feature gate string must not cause a parse error (covered by keeping the const in featureDefaults)

[Cloud-Architect-Emma]

@markmandel I am working on this issue, will link PR to fix issue once done.