Make it easier to use NextDNS or other private DNS server (#14288)

config.cfg

@@ -88,9 +88,15 @@ dnscrypt_servers:
   ipv4:
     - cloudflare
 #   - google
+#   - <YourCustomServer>  # E.g., if using NextDNS, this will be something like NextDNS-abc123.
+                          # You must also fill in custom_server_stamps below. You may specify
+                          # multiple custom servers.
   ipv6:
     - cloudflare-ipv6
 
+custom_server_stamps:
+# YourCustomServer: 'sdns://...'
+
 # DNS servers which will be used if 'dns_encryption' is 'false'.
 # Fallback resolvers for systemd-resolved
 # The default is to use Cloudflare.

roles/dns/templates/dnscrypt-proxy.toml.j2

@@ -551,5 +551,10 @@ cache_neg_max_ttl = 600
 
 [static]
 
+{% if custom_server_stamps %}{% for name, stamp in custom_server_stamps.items() %}
+  [static.'{{ name }}']
+  stamp = '{{ stamp }}'
+{%- endfor %}{% endif %}
+
   # [static.'myserver']
   # stamp = 'sdns:AQcAAAAAAAAAAAAQMi5kbnNjcnlwdC1jZXJ0Lg'