dns: add EDNS0 Padding option

[evverx]

https://datatracker.ietf.org/doc/html/rfc7830 specifies the EDNS(0) "Padding" option, which allows DNS clients and servers to pad request and response messages by a variable number of octets.

It was cross-checked with TShark

>>> tdecode(Ether()/IP()/UDP()/DNS(ar=[DNSRROPT(rdata=[EDNS0PADDING(padding=b'\x00')])]))
...
            Option: PADDING
                Option Code: PADDING (12)
                Option Length: 1
                Option Data: 00
                Padding: 00

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.30%. Comparing base (f4a2ca4) to head (636c2bd).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4959   +/-   ##
=======================================
  Coverage   80.30%   80.30%           
=======================================
  Files         379      379           
  Lines       93107    93167   +60     
=======================================
+ Hits        74769    74820   +51     
- Misses      18338    18347    +9     

Files with missing lines	Coverage Δ
scapy/layers/dns.py	83.67% <100.00%> (+0.05%)	⬆️

... and 5 files with indirect coverage changes

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