default on SameSite attribute unset for Oauth2 cookies

[arkodg]

Revisits https://github.com/envoyproxy/gateway/pull/6289 which had set SameSite=Strict. This may cause some issues for specific flows

I had misinterpresented the meaning of Disabled earlier, it means Unset, and is separate from Samesite=None

[arkodg]

cc @vibe

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 70.72%. Comparing base (3e14c49) to head (0192e03). Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6347      +/-   ##
==========================================
- Coverage   70.75%   70.72%   -0.03%     
==========================================
  Files         220      220              
  Lines       37103    37089      -14     
==========================================
- Hits        26253    26233      -20     
- Misses       9314     9317       +3     
- Partials     1536     1539       +3     

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[vibe]

Totally reasonable to default back to disabled / unset.

Thanks @arkodg

[shawnh2]

/retest