chore(release-1.6): upgrade Envoy to 1.21.3

[lobkovilya]

Signed-off-by: Ilya Lobkov ilya.lobkov@konghq.com

Summary

SUMMARY_GOES_HERE

Full changelog

• [Implement ...]
• [Fix ...]

Issues resolved

Fix #XXX

Documentation

• Link to the website documentation PR

Testing

• Unit tests
• E2E tests
• Manual testing on Universal
• Manual testing on Kubernetes

Backwards compatibility

• Update UPGRADE.md with any steps users will need to take when upgrading.
• Add backport-to-stable label if the code follows our backporting policy

[bartsmykla]

lgtm

[codecov-commenter]

Codecov Report

Merging #4457 (3220994) into release-1.6 (51582ed) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           release-1.6    #4457      +/-   ##
===============================================
- Coverage        55.78%   55.76%   -0.02%     
===============================================
  Files              932      932              
  Lines            56249    56249              
===============================================
- Hits             31378    31368      -10     
- Misses           22391    22399       +8     
- Partials          2480     2482       +2     

Impacted Files	Coverage Δ
pkg/plugins/leader/postgres/leader_elector.go	93.61% <0.00%> (-6.39%)	⬇️
pkg/api-server/server.go	85.35% <0.00%> (-2.93%)	⬇️

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