Promote ReferenceGrant to Beta

[robscott]

What would you like to be added:
Based on discussion in recent community meetings, we believe that ReferenceGrant has met the required graduation criteria to graduate to beta. This will require updating the types to match what we've done for GatewayClass, Gateway, and HTTPRoute, with one exception: The storage version will need to stick to v1alpha2 in this initial release.

[nathancoleman]

@robscott I can take this one

[robscott]

Thanks!

/assign @nathancoleman

[nathancoleman]

@robscott is the plan to move ReferenceGrant into the standard channel at the same time?

[robscott]

@nathancoleman yep, resources that have graduated to beta should also be part of the standard channel.