feat: Support for envoy gRPC v3 external authorization API

[dadrus]

Related issue(s)

closes #390

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

This PR implements support for Envoy ExtAuth v3 gRPC API and enables integration of heimdall with any Envoy based API Gateway, which support gRPC based integration of external authorization/authentication providers only. The only thing, which is required on heimdall side to have this integration working, is to start heimdall accordingly:

heimdall serve decision --envoy-grpc -c <path to your configuration>

That's all. No additional configuration required. If heimdall is started as shown above it will expose the gRPC service expected by Envoy, instead of the HTTP service, exposed if started without the --envoy-grpc flag. See also Quickstarts for working examples.

[codecov]

Codecov Report

Merging #469 (06f196e) into main (4cd30ab) will increase coverage by 0.28%.
The diff coverage is 91.82%.

@@            Coverage Diff             @@
##             main     #469      +/-   ##
==========================================
+ Coverage   88.50%   88.79%   +0.28%     
==========================================
  Files         194      206      +12     
  Lines        8038     8665     +627     
==========================================
+ Hits         7114     7694     +580     
- Misses        755      790      +35     
- Partials      169      181      +12     

Impacted Files	Coverage Δ
internal/handler/envoyextauth/grpcv3/module.go	17.64% <17.64%> (ø)
internal/accesscontext/access_context.go	90.00% <85.71%> (ø)
...extauth/grpcv3/middleware/accesslog/interceptor.go	87.87% <87.87%> (ø)
...nal/handler/envoyextauth/grpcv3/request_context.go	91.26% <91.26%> (ø)
internal/handler/envoyextauth/grpcv3/service.go	94.44% <94.44%> (ø)
...h/grpcv3/middleware/errorhandler/error_response.go	95.83% <95.83%> (ø)
...al/fiber/middleware/accesslog/accesslog_handler.go	95.65% <96.00%> (-0.94%)	⬇️
...auth/grpcv3/middleware/errorhandler/interceptor.go	98.33% <98.33%> (ø)
cmd/serve/decision.go	83.33% <100.00%> (+27.33%)	⬆️
...nal/fiber/middleware/errorhandler/error_handler.go	100.00% <100.00%> (ø)
... and 13 more

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