fix: Support allowlisted private API inbox webhooks (#14548)

Self-hosted installations can now opt SafeFetch into private-network
access after SSRF hardening. The default remains unchanged: private IP
destinations are blocked unless the instance owner explicitly enables
private-network requests with `SAFE_FETCH_ALLOW_PRIVATE_NETWORK=true`.

Fixes https://linear.app/chatwoot/issue/CW-7131
Fixes https://github.com/chatwoot/chatwoot/issues/14489
Fixes https://github.com/chatwoot/chatwoot/issues/14494

## How to use

For self-hosted installations that need API inbox webhooks, or other
SafeFetch-backed requests, to call trusted private services, enable
private-network access with a single environment variable:

```bash
SAFE_FETCH_ALLOW_PRIVATE_NETWORK=true
```

This is disabled by default. Enable it only when the instance owner
controls the deployment network and trusts the configured URLs.

lib/safe_fetch/private_network_request.rb

@@ -0,0 +1,102 @@
+class SafeFetch::PrivateNetworkRequest
+  def initialize(options)
+    @options = options
+  end
+
+  def perform(&)
+    url = options.url
+    original_url = url
+    original_uri = URI(url)
+
+    (SsrfFilter::DEFAULT_MAX_REDIRECTS + 1).times do
+      uri = URI(url)
+      validate_scheme!(uri)
+
+      response, next_url = fetch_once(uri, resolved_addresses(uri.hostname).sample.to_s, original_uri, &)
+      return response if next_url.nil?
+
+      url = next_url
+    end
+
+    raise SsrfFilter::TooManyRedirects, "Got #{SsrfFilter::DEFAULT_MAX_REDIRECTS} redirects fetching #{original_url}"
+  end
+
+  private
+
+  attr_reader :options
+
+  def validate_scheme!(uri)
+    return if SsrfFilter::DEFAULT_SCHEME_WHITELIST.include?(uri.scheme)
+
+    raise SsrfFilter::InvalidUriScheme, "URI scheme '#{uri.scheme}' not in whitelist: #{SsrfFilter::DEFAULT_SCHEME_WHITELIST}"
+  end
+
+  def resolved_addresses(hostname)
+    ip_addresses = options.resolver.call(hostname)
+    raise SsrfFilter::UnresolvedHostname, "Could not resolve hostname '#{hostname}'" if ip_addresses.empty?
+
+    ip_addresses
+  end
+
+  def fetch_once(uri, ip_address, original_uri, &)
+    request = build_request(uri)
+    strip_sensitive_headers!(request, original_uri, uri)
+    validate_request!(request)
+
+    Net::HTTP.start(uri.hostname, uri.port, **http_options(uri, ip_address)) do |http|
+      response = http.request(request, &)
+      return response, redirect_location(response, uri)
+    end
+  end
+
+  def build_request(uri)
+    request = SsrfFilter::VERB_MAP[options.method].new(uri)
+    request['host'] = normalized_hostname(uri)
+
+    Array(options.request_options[:headers]).each { |header, value| request[header] = value }
+    request.body = options.body if options.body
+    options.request_options[:request_proc].call(request) if options.request_options[:request_proc].respond_to?(:call)
+
+    request
+  end
+
+  def http_options(uri, ip_address)
+    options.request_options[:http_options].merge(
+      use_ssl: uri.scheme == 'https',
+      ipaddr: ip_address
+    )
+  end
+
+  def strip_sensitive_headers!(request, original_uri, uri)
+    return unless different_origin?(original_uri, uri)
+
+    options.request_options[:sensitive_headers].each { |header| request.delete(header) }
+  end
+
+  def validate_request!(request)
+    request.each do |header, value|
+      next if header.count("\r\n").zero? && value.count("\r\n").zero?
+
+      raise SsrfFilter::CRLFInjection, "CRLF injection in header #{header} with value #{value}"
+    end
+  end
+
+  def redirect_location(response, uri)
+    return unless response.is_a?(Net::HTTPRedirection)
+
+    location = response['location']
+    return "#{uri.scheme}://#{normalized_hostname(uri)}#{location}" if location&.start_with?('/')
+
+    location
+  end
+
+  def normalized_hostname(uri)
+    return uri.hostname if (uri.port == 80 && uri.scheme == 'http') || (uri.port == 443 && uri.scheme == 'https')
+
+    "#{uri.hostname}:#{uri.port}"
+  end
+
+  def different_origin?(uri, other_uri)
+    uri.scheme != other_uri.scheme || uri.hostname != other_uri.hostname || uri.port != other_uri.port
+  end
+end