feat(gateway): set cluster HTTP2 stream and connection window size

[michaelbeaumont]

Part of #4692

Checklist prior to review

• Link to docs PR or issue --
• Link to UI issue or PR --
• Is the issue worked on linked? --
• Unit Tests --
• E2E Tests -- none
• Manual Universal Tests -- none
• Manual Kubernetes Tests -- none
• Do you need to update UPGRADE.md? -- no
• Does it need to be backported according to the backporting policy? -- no

[codecov-commenter]

Codecov Report

Merging #4779 (5901eee) into master (ecdf217) will increase coverage by 0.00%.
The diff coverage is 50.00%.

@@           Coverage Diff           @@
##           master    #4779   +/-   ##
=======================================
  Coverage   46.42%   46.42%           
=======================================
  Files         690      690           
  Lines       46998    47002    +4     
=======================================
+ Hits        21817    21819    +2     
- Misses      23256    23257    +1     
- Partials     1925     1926    +1     

Impacted Files	Coverage Δ
pkg/xds/envoy/clusters/v3/http2_configurer.go	76.92% <40.00%> (-23.08%)	⬇️
pkg/plugins/runtime/gateway/cluster_generator.go	91.72% <100.00%> (ø)
pkg/xds/generator/direct_access_proxy_generator.go	90.90% <0.00%> (+1.13%)	⬆️

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