[fix](docker) dcr fe stop grace

[catpineapple]

What problem does this PR solve?

Issue Number: close #xxx

Related PR: #xxx

Problem Summary:

Release note

None

Check List (For Author)

• Test

  • Regression test
  • Unit Test
  • Manual test (add detailed scripts or steps below)
  • No need to test or manual test. Explain why:
    • This is a refactor/code format and no logic has been changed.
    • Previous test can cover this change.
    • No code files have been changed.
    • Other reason

• Behavior changed:

  • No.
  • Yes.

• Does this need documentation?

  • No.
  • Yes.

Check List (For Reviewer who merge this PR)

• Confirm the release note
• Confirm test cases
• Confirm document
• Add branch pick label

[hello-stephen]

Thank you for your contribution to Apache Doris.
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Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?

[github-actions]

PR approved by at least one committer and no changes requested.

[github-actions]

PR approved by anyone and no changes requested.

[CalvinKirs]

LGTM

[hello-stephen]

skip buildall

[hello-stephen]

/review

[github-actions]

No blocking issues found in this PR.

Critical checkpoint conclusions:

• Goal of the task: The change makes the standard FE Kubernetes preStop hook use graceful shutdown, matching the existing fe_disaggregated_prestop.sh and BE preStop behavior. The code accomplishes that goal. No automated test is included in the PR, so this remains validated by code-path consistency rather than an executed test.
• Scope and clarity: The modification is minimal, clear, and focused to a single call site in docker/runtime/fe/resource/fe_prestop.sh.
• Concurrency: Not applicable. This is a shell shutdown hook with no shared in-process concurrency logic.
• Lifecycle management: No special lifecycle or static initialization concerns apply here.
• Configuration changes: None.
• Compatibility: No incompatible API, storage, or protocol change is introduced. stop_fe.sh already supports --grace.
• Parallel code paths: Applicable and handled well. This change brings the standard FE preStop path in line with the already-graceful disaggregated FE and BE preStop scripts.
• Special conditional checks: None added.
• Test coverage: No dedicated regression/unit test was added. For this shell-script change that is understandable, but manual validation in a containerized shutdown path would still be useful.
• Observability: Existing logging in fe_prestop.sh remains sufficient for this small change.
• Transaction/persistence/data-write impact: None directly.
• Performance: No concern.
• Other issues: None identified from the modified code path.

Overall opinion: the patch is small, consistent with adjacent shutdown scripts, and looks correct.