Updating contribution guidelines

[gpotter2]

Hi everyone !

This is a change to update the contribution guidelines for Scapy. Those are probably not final and might get updated, but we're trying to introduce some meaningful guidelines regarding the involvement of AI.

This PR:

• introduces a new commit requirement. We mimic what Wireshark has done, by requiring a AI-Assisted: yes/no [tool] tag on each commit. I know, it's a bit annoying, but it's probably less aggressive than having to shout at people in the PR template and the contributing guidelines. I think that for maintainers, it's a really nice approach.
• updates the PR template to be less verbose

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.28%. Comparing base (622b220) to head (fba6a4b).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4993   +/-   ##
=======================================
  Coverage   80.28%   80.28%           
=======================================
  Files         383      383           
  Lines       94739    94739           
=======================================
+ Hits        76060    76063    +3     
+ Misses      18679    18676    -3     

see 10 files with indirect coverage changes

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