[INLONG-8649][Agent] Fix the proxysink thread leaks when the dataproxy sdk init failed

[justinwwhuang]

fix bug: proxysink thread leaks when the dataproxy sdk init failed

Prepare a Pull Request

• Fixes [Bug][Agent] Thread leaks for ProxySink when the DataProxy SDK init failed #8649

Motivation

proxysink thread leaks when the dataproxy sdk init failed

Modifications

start the thread after the sender has manager start

Verifying this change

(Please pick either of the following options)

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

• This change is already covered by existing tests, such as:
  (please describe tests)

• This change added tests and can be verified as follows:

  (example:)

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

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)
• If a feature is not applicable for documentation, explain why?
• If a feature is not documented yet in this PR, please create a follow-up issue for adding the documentation