feat(meshgateway): create MADR for deployment customization

[johnharris85]

Changelog: feat(MeshGateway): support deployment customization for MeshGatewayInstance

Checklist prior to review

• Link to relevant issue as well as docs and UI issues --
• This will not break child repos: it doesn't hardcode values (.e.g "kumahq" as a image registry) and it will work on Windows, system specific functions like syscall.Mkfifo have equivalent implementation on the other OS --
• Tests (Unit test, E2E tests, manual test on universal and k8s) --
• Do you need to update UPGRADE.md? --
• Does it need to be backported according to the backporting policy? --
• Do you need to explicitly set a > Changelog: entry here or add a ci/ label to run fewer/more tests?

[bartsmykla]

I'm not sure if having serviceTemplate inside MeshGatewayInstance spec and DeploymentTemplate as a separate "resource" is a good idea. I don't see reason why serviceTemplate would be in one place and DeploymentTemplate in other

We created a ContainerPatch as a separate policy as on Kubernetes Dataplane resource is automatically created from k8s' services/pods. If it would be manually created, I think we would put the "patch" inside of the Dataplane manifest instead of creating separate policy (especially as it's valid only for Kubernetes)

I think I would prefer to have deploymentTemplate inside MeshGatewayInstance instead of creating separate resource.

Edit: I just realized, that you might not mean to create a separate DeploymentTemplate resource as a policy, but when you said "object" you meant just an abstraction, which we could place inside MeshGatewayInstance. Am I right?

I think we have good abstractions in place to work with json patches (especially as they were abstracted in #6281), so I would suggest to rethink if we just don't want to reuse them and go with the option similar to ContainerPatches

[johnharris85]

Edit: I just realized, that you might not mean to create a separate DeploymentTemplate resource as a policy, but when you said "object" you meant just an abstraction, which we could place inside MeshGatewayInstance. Am I right?

Yep :)

I think we have good abstractions in place to work with json patches (especially as they were abstracted in #6281), so I would suggest to rethink if we just don't want to reuse them and go with the option similar to ContainerPatches

Agree, and long-term I'd like to go this way (see #6347) but this would be a short-term fix which follows the same pattern as serviceTemplate.

[lahabana]

It's an ok way to get started. We can always do better in the future