ddns-scripts: add blazingfast.io Anycast DNS provider

ddns-scripts: add blazingfast.io Anycast DNS provider

Add DDNS update support for blazingfast.io Anycast DNS via their
REST API. Authentication is performed via JWT token obtained from
the login endpoint. Zone records are fetched to verify the record
type before update, ensuring IPv4 services only target A records
and IPv6 services only target AAAA records.

Service, zone and record IDs are passed via param_opt as
space-separated key=value pairs:
  service_id=X zone_id=Y record_id=Z

curl --config file approach is used throughout to avoid eval and
shell injection from user-controlled values. Supports both IPv4
and IPv6. For dual-stack, create two separate DDNS service sections
with their respective record IDs.

Tested on GL.iNet MT5000 (Brume 3) running OpenWrt with
ddns-scripts 2.8.2.

Signed-off-by: Fotios Kitsantas <redacted>