Add SGlang example/docs

[rahulgurnani]

What type of PR is this?

/kind documentation

What this PR does / why we need it:
SGlang is one of the most popular model server. It is good for users to have better documentation around it of how to deploy sglang with IGW.

Which issue(s) this PR fixes:

Fixes #1141

Does this PR introduce a user-facing change?:

Add sample deployment and docs about sglang support

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[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: rahulgurnani
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