feat(docs): add gotify example using webhook custom payload - #5408

#!/bin/bash
set -eu

printf '%s\n' '--- target file ---'
cat -n examples/webhook/gotify.yml

printf '%s\n' '--- repository references to webhook timeout and Gotify ---'
rg -n -i -C 3 'timeout:|webhook_configs|gotify|group_interval' \
  examples docs README.md .github 2>/dev/null || true

printf '%s\n' '--- repository metadata ---'
rg -n '"(alertmanager|prometheus[^"]*)"|alertmanager' \
  package.json go.mod go.sum Makefile README.md 2>/dev/null || true

#!/bin/bash
set -eu

printf '%s\n' '--- webhook configuration and delivery symbols ---'
rg -n -i -C 5 'type WebhookConfig|WebhookConfig|webhook.*timeout|Timeout.*webhook|DoRequest|context.WithTimeout|group_interval|notification.*context' \
  . --glob '*.go' --glob '*.md' --glob '*.yml' --glob '*.yaml' 2>/dev/null | head -n 500

printf '%s\n' '--- candidate Go files ---'
rg -l -i 'webhook.*timeout|type WebhookConfig|context.WithTimeout|group_interval' \
  --glob '*.go' .

#!/bin/bash
set -eu

printf '%s\n' '--- webhook implementation ---'
cat -n notify/webhook/config.go
sed -n '1,280p' notify/webhook/webhook.go

printf '%s\n' '--- dispatch notification context ---'
sed -n '760,845p' dispatch/dispatch.go

printf '%s\n' '--- webhook timeout integration test ---'
sed -n '520,590p' test/with_api_v2/acceptance/send_test.go

#!/bin/bash
set -eu
file=$(fd -t f '^gotify\.yml$' . | head -n 1)
printf '%s\n' "FILE=$file"
cat -n "$file" | sed -n '1,100p'
printf '%s\n' '--- Gotify-related references ---'
rg -n -i 'gotify|text/markdown|client::display|msgextras' . -g '!node_modules' -g '!dist' -g '!build' | head -n 200

#!/bin/bash
set -eu
printf '%s\n' '--- Related documentation ---'
cat -n docs/notification_examples.md | sed -n '155,185p'
printf '%s\n' '--- Template and escaping references ---'
rg -n -i 'text/template|html/template|escaping|annotations|labels.*template|template.*annotations' docs template *.go */*.go 2>/dev/null | head -n 200

python3 - <<'PY'
from pathlib import Path
import re

path = Path("examples/webhook/gotify.yml")
text = path.read_text()
body = text.split("          message: |", 1)[1]

fields = re.findall(r"\{\{\s*([^{}]+?)\s*\}\}", body)
print("Interpolated fields:")
for field in fields:
    print("-", field.strip())

# Demonstrate that the template places alert-controlled annotation data
# directly inside Markdown without escaping.
rendered = body.replace("{{ .Annotations.summary }}", "ok ![tracking](https://attacker.example/pixel)")
print("\nInjected Markdown survives:")
for line in rendered.splitlines():
    if "tracking" in line:
        print(line.strip())
PY