fix dead links to CCSDS 727.0-B-4 standard document (#1614)

* fix dead links to the CCSDS 727.0-B-4 standard document

CCSDS 727.0-B-4 is now a historical document and available at https://public.ccsds.org/Pubs/727x0b4s.pdf
since july 2020 the new CCSDS 727.0-B-5 is vaild and available at https://public.ccsds.org/Pubs/727x0b5.pdf

* Update sdd.md

Fw/FilePacket/docs/sdd.md

@@ -11,7 +11,7 @@ It represents an ISF file packet.
 The file packet format is similar to the Protocol Data Unit (PDU) format
 defined in the CCSDS File Delivery Protocol (CFDP).
 See § 5 of the
-[CCSDS File Delivery Protocol (CFDP) Recommended Standard](http://public.ccsds.org/publications/archive/727x0b4.pdf).
+[CCSDS File Delivery Protocol (CFDP) Recommended Standard](https://public.ccsds.org/Pubs/727x0b4s.pdf).
 
 Each file packet contains the following data: