[branch-4.0][fix](security) Add auth and config gate for _stream_load_forward endpoint

[liaoxin01]

Pick #64935

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[Copilot]

Pull request overview

This PR (cherry-picking #64935 into branch-4.0) hardens the BE _stream_load_forward endpoint used by cloud group-commit stream load forwarding by adding a BE-side config gate and wiring the handler through an auth-capable HTTP handler.

Changes:

• Add a BE config flag enable_group_commit_streamload_be_forward (default false) to gate the _stream_load_forward endpoint.
• Switch _stream_load_forward handler to HttpHandlerWithAuth and pass ExecEnv during registration.
• Update the regression suite to enable the new BE config for stream load forward.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
regression-test/suites/load_p0/stream_load/test_group_commit_redirect.groovy	Enables BE-side config needed for _stream_load_forward in the dockerized regression cluster.
be/src/service/http_service.cpp	Registers _stream_load_forward handler with ExecEnv so auth-capable handler can be constructed.
be/src/http/action/stream_load_forward_handler.h	Converts the handler to inherit from HttpHandlerWithAuth and sets initial privilege requirements.
be/src/http/action/stream_load_forward_handler.cpp	Adds config gate + invokes HttpHandlerWithAuth during header processing.
be/src/common/config.h	Declares new BE config enable_group_commit_streamload_be_forward.
be/src/common/config.cpp	Defines new BE config enable_group_commit_streamload_be_forward with default false.

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[liaoxin01]

run buildall