fix(xds): preserve original host metadata for DFP rewrites

[officialasishkumar]

What type of PR is this?
fix(xds): preserve original host metadata for DFP rewrites

What this PR does / why we need it:
Dynamic forward proxy host rewrites were clearing the route-level host rewrite metadata after the per-route DFP config was added. That left Envoy without the router-level information it uses to emit X-ENVOY-ORIGINAL-HOST, even though the rewritten host still drove DNS resolution. This change keeps the route host rewrite metadata in place, adds a focused regression test for both header and literal rewrites, and updates the translator golden output accordingly.

Which issue(s) this PR fixes:
Fixes #8353

Release Notes: Yes

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[zirain]

are you sure that this fixed the issue?

[officialasishkumar]

@zirain yes

[zirain]

@zirain yes

I tested it locally, and it didn't find it worked(maybe i missed something).
So I would like to see an worked e2e.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.32%. Comparing base (b1d7302) to head (f6a5cbc).
⚠️ Report is 139 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8610      +/-   ##
==========================================
+ Coverage   74.29%   74.32%   +0.02%     
==========================================
  Files         243      243              
  Lines       38155    38150       -5     
==========================================
+ Hits        28347    28354       +7     
+ Misses       7815     7806       -9     
+ Partials     1993     1990       -3     

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[zhaohuabing]

I haven’t verified this yet, but I’d expect X-ENVOY-ORIGINAL-HOST to reflect the DFP-rewritten host rather than the client’s original host, since the DFP filter updates the Host header before the request reaches the router.

This may require a change on the Envoy side to have the DFP filter set this header.

cc @wbpcode, who has more context here.

[github-actions]

This pull request has been automatically marked as stale because it has not had activity in the last 30 days. Please feel free to give a status update now, ping for review, when it's ready. Thank you for your contributions!