[INLONG-6833][Doc] Add doris and starrocks load node in README.md

[liaorui]

Prepare a Pull Request

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• Title Example: [INLONG-XYZ][Component] Title of the pull request

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• Fixes [Feature][Doc]Data Load Node lost Doris and StarRocks in README.md  #6833

Motivation

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Modifications

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Verifying this change

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• This change is a trivial rework/code cleanup without any test coverage.

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  (please describe tests)

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  • Added integration tests for end-to-end deployment with large payloads (10MB)
  • Extended integration test for recovery after broker failure

Documentation

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