feat: Configuration for read and write buffer sizes

[dadrus]

Related issue(s)

closes #704

Checklist

• I agree to follow this project's Code of Conduct.
• I have read, and I am following this repository's Contributing Guidelines.
• I have read the Security Policy.
• I have referenced an issue describing the bug/feature request.
• I have added tests that prove the correctness of my implementation.
• I have updated the documentation.

Description

Introduces a new property to define the read and write buffer sizes for the incoming request and the outgoing responses. The following property is supported for all services exposed by heimdall, so the decision, the proxy and the management service:

buffer_limit:
  read: 1MB
  write: 10KB

[codecov]

Codecov Report

Merging #706 (db3dd20) into main (b6af883) will increase coverage by 0.01%.
The diff coverage is 88.23%.

@@            Coverage Diff             @@
##             main     #706      +/-   ##
==========================================
+ Coverage   89.47%   89.48%   +0.01%     
==========================================
  Files         213      213              
  Lines        9072     9103      +31     
==========================================
+ Hits         8117     8146      +29     
- Misses        764      765       +1     
- Partials      191      192       +1     

Impacted Files	Coverage Δ
internal/config/parser/merge.go	91.11% <0.00%> (-4.35%)	⬇️
internal/config/serve.go	100.00% <ø> (ø)
internal/config/configuration.go	100.00% <100.00%> (ø)
internal/config/default_configuration.go	100.00% <100.00%> (ø)
internal/config/mapstructure_decoder.go	97.61% <100.00%> (+0.28%)	⬆️
internal/handler/decision/app.go	100.00% <100.00%> (ø)
internal/handler/envoyextauth/grpcv3/service.go	94.64% <100.00%> (+0.19%)	⬆️
internal/handler/management/app.go	76.74% <100.00%> (+1.13%)	⬆️
internal/handler/proxy/app.go	80.76% <100.00%> (+0.76%)	⬆️

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