infra: support reloadable EnvoyGateway configuration

[zirain]

fixes: #3209

[codecov]

Codecov Report

Attention: Patch coverage is 11.01695% with 210 lines in your changes missing coverage. Please review.

Project coverage is 65.53%. Comparing base (958df48) to head (b5f5749).

Files with missing lines	Patch %	Lines
...nternal/envoygateway/config/loader/configloader.go	0.00%	54 Missing ⚠️
internal/infrastructure/runner/runner.go	0.00%	42 Missing ⚠️
internal/cmd/server.go	0.00%	26 Missing ⚠️
internal/provider/runner/runner.go	0.00%	18 Missing ⚠️
internal/gatewayapi/runner/runner.go	12.50%	14 Missing ⚠️
internal/globalratelimit/runner/runner.go	33.33%	14 Missing ⚠️
internal/xds/server/runner/runner.go	33.33%	14 Missing ⚠️
internal/extension/registry/extension_manager.go	0.00%	13 Missing ⚠️
internal/xds/translator/runner/runner.go	20.00%	11 Missing and 1 partial ⚠️
internal/provider/kubernetes/kubernetes.go	77.77%	2 Missing ⚠️
... and 1 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4299      +/-   ##
==========================================
- Coverage   65.80%   65.53%   -0.27%     
==========================================
  Files         200      201       +1     
  Lines       24277    24396     +119     
==========================================
+ Hits        15976    15989      +13     
- Misses       7159     7268     +109     
+ Partials     1142     1139       -3     

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[zirain]

failed because ExtensionAPISettings didn't updated. It's able to add new watcher after EnvoyGateway updated, but cannot remove watcher after EnvoyGateway updated.

[zhaohuabing]

Dealing with configuration reload for each runner can be cumbersome, especially as the EnvoyGateway may introduce additional settings in the future. Would it be more straightforward to restart all runners instead of reloading the configuration individually?

[zirain]

close this first in favor of #4451, maybe came back later.