replace MeshGateway with a namespaced MeshBuiltinGateway

[lahabana]

Description

Maybe MeshBuiltinGateway is the right name.

Or maybe we have a general Gateway object to deal with provided gw too.

We'd need a way to restrict route attachment like Gateway API's allowedRoutes

[lobkovilya]

additional context from @michaelbeaumont

the one thing you can't do, either now or with namespaced MeshBuiltinGateway, is give permission for a strict subset of namespaces. like if I want to expose a gateway to route traffic to payments and orders I have to create a MeshGateway/kuma-system MeshBuiltinGateway, but either way, I still need kuma-system Routes. I can't give someone from payments/orders the option to only expose both payments/orders, so you always have to go through the mesh operator.

for the namespaced MeshBuiltinGateway to be truly more useful I think you'd need ReferenceGrant. so you could create a payments MeshBuiltinGateway, create payments routes and create a orders ReferenceGrant allowing refs from payments

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[github-actions]

This issue was inactive for 90 days. It will be reviewed in the next triage meeting and might be closed.
If you think this issue is still relevant, please comment on it or attend the next triage meeting.