Provide instructions on revisioned upgrade of east-west gateway

[jasonwzm]

Describe the feature request
The eastwest gateway is currently revisioned, but because it is not installed with istioctl, the upgrade experience is not well documented. We need to document that in docs.

Later if we move it in a separate profile, it can be better handled by istioctl.

/cc @nmittler @stevenctl @duderino

Describe alternatives you've considered

[X] Docs
[ ] Installation
[ ] Networking
[ ] Performance and Scalability
[ ] Extensions and Telemetry
[ ] Security
[ ] Test and Release
[ ] User Experience
[ ] Developer Infrastructure

Additional context

[nmittler]

@jasonwzm is this still something you're working on?

[jasonwzm]

@nmittler Thanks for the reminder on this. Have we talked about injection-based east-west gateway vs revisioned gateway? With the injection based gateway more in the picture, it might be also worth it to assess which option we provide.

[nmittler]

IIRC the direction so far has been revisioned gateways.

@stevenctl can you confirm?

[stevenctl]

I agree with using revisioned gateways. I do think there's an opportunity to simplify the installation process using injection as well. #34835

[istio-policy-bot]

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