[branch-4.1][fix](security) Add auth and config gate for _stream_load_forward endpoint

[liaoxin01]

Pick #64935

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1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
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[Copilot]

Pull request overview

This PR backports a security fix to the BE _stream_load_forward endpoint by adding an explicit BE-side config gate and wiring the endpoint into the existing HTTP auth framework, aligning it with cloud group-commit forwarding behavior.

Changes:

• Gate /api/{db}/{table}/_stream_load_forward behind enable_group_commit_streamload_be_forward (default false) in BE.
• Require HTTP auth for the forward handler by converting it to HttpHandlerWithAuth and passing ExecEnv from HttpService.
• Update the regression test cluster config to enable the feature flag on both FE and BE.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
regression-test/suites/load_p0/stream_load/test_group_commit_redirect.groovy	Enables the new BE config gate in the regression test cluster setup.
be/src/service/http/action/stream_load_forward_handler.h	Switches the handler base class to HttpHandlerWithAuth and adds an ExecEnv* constructor.
be/src/service/http/action/stream_load_forward_handler.cpp	Adds the runtime config gate and calls the auth hook in on_header.
be/src/service/http_service.cpp	Constructs the forward handler with _env (required for auth).
be/src/common/config.h	Declares the new BE config enable_group_commit_streamload_be_forward.
be/src/common/config.cpp	Defines the new BE config with default false.

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[liaoxin01]

run buildall