Require Gateway APIs for related perms and release 2.8.1

[rainest]

What this PR does / why we need it:

Only create Gateway APIs rules in RBAC roles if Gateway API CRDs are present on the cluster. This avoids installation failures when installers lack super-admin, and will not have permission to create roles that can access these resources.

Releases 2.8.1 with this and the other pending hotfix.

Kubernetes RBAC limits the role creation permission to creating roles that the account used to create the role already has itself. Roles are very unlikely to include permissions for Gateway APIs if Gateway API CRDs are not installed.

Reported in community Slack channel https://kubernetes.slack.com/archives/CDCA87FRD/p1652461006349149

Special notes for your reviewer:

Checklist

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• PR is based off the current tip of the main branch.
• Changes are documented under the "Unreleased" header in CHANGELOG.md
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