[feat](nereids) add is_merge tag for data sink

[englefly]

What problem does this PR solve?

set is_merge true, if its corresponding exchange node contains sortInfo.
BE use this flag to accelerate data transferring.

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

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[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[englefly]

run buildall

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[github-actions]

PR approved by anyone and no changes requested.

[github-actions]

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

[englefly]

it is better to determine this by FE than that by BE.
for example, if data spill to disk, the node before sink is scan, not sort