fix(chart): route hubble ui api via grpc_pass

[abdullazin]

Summary

• fix the Hubble UI /api path in nginx by switching from proxy_pass to grpc_pass
• preserve existing baseUrl rewrite logic
• keep the fix scoped to nginx template behavior (no extra backend service/routing objects)

Why this change

• with Envoy in front of Hubble UI, the UI data stream call to /api/ui.UI/GetEvents was failing with HTTP 400
• the UI surfaced this as: Data stream has failed on the UI backend: Http response at 400 or 500 level, http status code: 400
• the backend response included: grpc-message: gRPC requires HTTP/2
• this indicates the /api path needed to be handled as gRPC traffic at the nginx hop

Path handling note

• a gRPC request carries its route in the :path pseudo-header
• grpc_pass does not rewrite request path based on upstream URI suffix
• therefore the conditional grpc://127.0.0.1:8090 vs grpc://127.0.0.1:8090/ is unnecessary
• this PR simplifies to a single grpc_pass grpc://127.0.0.1:8090;

Files

• deploy/hubble/manifests/controller/helm/retina/templates/hubble-ui/_nginx.tpl

Verification

• rendered chart templates locally after the nginx change
• confirmed only _nginx.tpl changed in this PR branch

[abdullazin]

@microsoft-github-policy-service agree [company="GoTo"]

[abdullazin]

@microsoft-github-policy-service agree company="GoTo"

[abdullazin]

@nairashu or @alam-tahmid , can you please review my PR?