internal/dag: configure 502 if include references another (#5016)

[liangyuanpeng]

Set 502 response if include references another root

Fixes #5016

[github-actions]

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[codecov]

Codecov Report

Merging #5157 (c383eb0) into main (eb2b000) will increase coverage by 0.00%.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5157   +/-   ##
=======================================
  Coverage   77.90%   77.91%           
=======================================
  Files         138      138           
  Lines       17856    17861    +5     
=======================================
+ Hits        13911    13916    +5     
  Misses       3675     3675           
  Partials      270      270           

Impacted Files	Coverage Δ
internal/dag/httpproxy_processor.go	92.33% <100.00%> (+0.03%)	⬆️

[sunjayBhatia]

thanks for the PR, implementation looks great, just needs

• some test coverage (similar to this test case, but with an include that references a "root" httpproxy:

  contour/internal/dag/builder_test.go

  Line 10611 in aa750df

  "insert httproxy with invalid include": {

  )
• and a release note (following guidelines here https://github.com/projectcontour/contour/blob/aa750df6bce7f6a46ff3739cc9f935f1134c0500/CONTRIBUTING.md#commit-message-and-pr-guidelines, in this case a small release note type)

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[sunjayBhatia]

the test failure should be resolved by merging/rebasing main and swapping the Listener port in the test to 8080, that was a change that occurred on main more recently