fix: set observedGeneration in envoy patch policy

[kkk777-7]

What this PR does / why we need it:
Fixed that observedGeneration is missing from the EnvoyPatchPolicy status condition.
Introduce new field in IR to set observedGeneration.

Which issue(s) this PR fixes:

Fixes #7713

Release Notes: Yes

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.29%. Comparing base (b9123a8) to head (661d494).
⚠️ Report is 9 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7715   +/-   ##
=======================================
  Coverage   72.28%   72.29%           
=======================================
  Files         234      234           
  Lines       34480    34481    +1     
=======================================
+ Hits        24924    24928    +4     
+ Misses       7767     7764    -3     
  Partials     1789     1789           

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[kkk777-7]

The changes in the xDS translate output message are likely due to modifying the processing order in translator_test.go to reflect the translation results in the policy status.

In the current code on the main branch, the test case for errMsg returns early.
https://github.com/envoyproxy/gateway/blob/main/internal/xds/translator/translator_test.go#L183-L191
Therefore, I assume that when the policy message was updated, the changes were not reflected in the test output.

[kkk777-7]

/retest

[arkodg]

LGTM thanks

[zirain]

/retest