Translation: return 500 when CTP translation fails

[zhaohuabing]

• Return a 503 response when a ClientTrafficPolicy translation fails for HTTP/GRPC routes.
• Route client traffic to an empty dummy cluster when a ClientTrafficPolicy translation fails for TCP routes.

Implements: #4153
Release Notes: Yes

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.82%. Comparing base (00ed0b8) to head (8c1b088).
Report is 11 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5030      +/-   ##
==========================================
+ Coverage   66.75%   66.82%   +0.06%     
==========================================
  Files         209      209              
  Lines       32409    32417       +8     
==========================================
+ Hits        21636    21663      +27     
+ Misses       9468     9452      -16     
+ Partials     1305     1302       -3     

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[arkodg]

LGTM thanks !