feat(blink-lnurl-server): add ingress.annotations passthrough

[pretyflaco]

Summary

Add an optional ingress.annotations passthrough to the blink-lnurl-server chart so operators can attach nginx ingress annotations via values, without forking the vendored chart.

Motivation

We need to apply path-scoped rate limiting to lnurl.blink.sv/verify/* (see blinkbitcoin/blink-wip#1123 — runaway LUD-21 verify polling from BTCPay plugins). The rate limit is implemented as an ingress-nginx server-snippet annotation on the lnurl-server Ingress, but the chart currently hardcodes its annotations block with no passthrough.

Change

• templates/ingress.yaml: merge .Values.ingress.annotations under the existing cert-manager.io/cluster-issuer default.
• values.yaml: document the new ingress.annotations field (default {}).

Fully backward-compatible: when ingress.annotations is unset the rendered manifest is unchanged.

Validation

Rendered locally with helm template:

annotations:
  cert-manager.io/cluster-issuer: letsencrypt-issuer
  nginx.ingress.kubernetes.io/server-snippet: location ~ ^/verify/ { return 429; }

The companion blinkbitcoin/blink-deployments change (staging) wires the actual rate-limit zone + snippet.