Ensures Gateway-API object fields obey kubebuilder max item validation

[carmal891]

What type of PR is this?
/kind feature

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #124

Does this PR introduce a user-facing change?:

Added validation for Gateway API maxItems constraints. Now returns appropriate error messages when field limits are exceeded during I2GW conversion

[k8s-ci-robot]

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