fix(hubble): bump default hubble-relay image

[holly-agyei]

Summary

• bump the default retina-hubble hubble-relay image from v1.15.0 to 1.16.1
• align the optional relay digest with the current 1.16.1 MCR manifest
• update the Hubble Relay Deployment to use the shared cilium.image helper so override, useDigest, and digest are honored

Fixes #2165.

Verification

• confirmed MCR exposes 1.16.1 for oss/cilium/hubble-relay
• confirmed the 1.16.1 manifest digest is sha256:641b13bbe9038d7b0bedd6480e3d704174432e1fd05a25728a4eb27ec47df89a
• verified the Hubble Relay Deployment now renders its image via the shared cilium.image helper

[Copilot]

Pull request overview

This PR updates the default hubble-relay container image used by the retina-hubble Helm chart to a newer upstream version to restore ALPN/h2 support needed by newer grpc-go (and thus Hubble CLI).

Changes:

• Bump default hubble-relay image tag from v1.15.0 to 1.16.1.
• Update the configured digest to match the 1.16.1 MCR manifest digest.

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[Copilot]

The hubble-relay image digest, useDigest, and override fields in values are currently ineffective: the hubble-relay Deployment template renders the image as {{ .Values.hubble.relay.image.repository }}:{{ .Values.hubble.relay.image.tag }} and never uses these keys. As a result, updating the digest here won’t actually pin the hubble-relay image. Consider updating the hubble-relay template to use the existing cilium.image helper (or otherwise conditionally append @<digest> when useDigest is true and honor override).