feat(Istio): integrate with Istio gateway via extproc

[srampal]

What type of PR is this?

• "feat(translator): add new feature"

What this PR does / why we need it:
This PR enables Semantic Router to work with Istio Envoy gateway via the ExtProc interface between Istio and Semantic Router

Which issue(s) this PR fixes:
This is one of multiple fixes needed for the issue #39. There will also be additional PRs needed in order to complete that issue/ Feature.

Release Notes: Yes

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[srampal]

I have tested .. this is working correctly with Istio based Envoy gateway.

[Xunzhuo]

1. can you create a sparate dir under kubernetes like kubernetes/istio/xxx.yaml to put resource related istio?
2. can you provide steps you install in kuberenetes with istio?

[srampal]

1. can you create a sparate dir under kubernetes like kubernetes/istio/xxx.yaml to put resource related istio?
2. can you provide steps you install in kuberenetes with istio?

I was planning to add the istio docs as a separate PR .. anyway .. but sure .. will add that now via this PR.

[srampal]

@Xunzhuo @rootfs fyi I'm still working on updating this commit and running into some issues so am working on troubleshooting those. Should have an update in a couple of days.

[srampal]

1. can you create a sparate dir under kubernetes like kubernetes/istio/xxx.yaml to put resource related istio?
2. can you provide steps you install in kuberenetes with istio?

Done. And also updated the solution. I have tested that the PR works: Semantic Router using Istio-Envoy Gateway as the front-end via ExtProc without any other gateway. Please review/ approve. @rootfs @Xunzhuo @wangchen615