feature: http buffer filter configuration (#6249)

[ruzmuh]

Proposal for Issue #6249:
Introduce two optional command line flags, envoy-http-buffer-max-request-bytes and envoy-https-buffer-max-request-bytes, with default values set to 0. If the value is non-zero, an HTTP buffer filter will be added to the HTTP filter chain immediately after the DefaultFilters() with the max_request_bytes parameter. This configuration allows setting the buffer filter for the entire HTTP listener. In the future, it possible to provide ability to override these values on a per-route basis using bufferperroute.

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[codecov]

Codecov Report

Attention: Patch coverage is 94.11765% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 81.57%. Comparing base (c3d6cb4) to head (fba7631).
Report is 43 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6315   +/-   ##
=======================================
  Coverage   81.56%   81.57%           
=======================================
  Files         133      134    +1     
  Lines       15801    15828   +27     
=======================================
+ Hits        12888    12911   +23     
- Misses       2617     2621    +4     
  Partials      296      296           

Files	Coverage Δ
cmd/contour/servecontext.go	86.02% <100.00%> (+0.07%)	⬆️
internal/contourconfig/contourconfiguration.go	98.70% <100.00%> (+0.01%)	⬆️
internal/envoy/v3/buffer.go	100.00% <100.00%> (ø)
internal/xdscache/v3/listener.go	92.06% <100.00%> (+0.05%)	⬆️
pkg/config/parameters.go	88.07% <100.00%> (+0.04%)	⬆️
cmd/contour/serve.go	22.59% <0.00%> (-0.07%)	⬇️

... and 5 files with indirect coverage changes