[Feature] support set_var hint for DML (backport #35283)

[mergify]

Why I'm doing:

• The SET_VAR hint is only viable for query, but not DML

What I'm doing:

• Support set_var for insert/update/delete sql

Fixes #issue

What type of PR is this:

• BugFix
• Feature
• Enhancement
• Refactor
• UT
• Doc
• Tool

Does this PR entail a change in behavior?

• Yes, this PR will result in a change in behavior.
• No, this PR will not result in a change in behavior.

If yes, please specify the type of change:

• Interface/UI changes: syntax, type conversion, expression evaluation, display information
• Parameter changes: default values, similar parameters but with different default values
• Policy changes: use new policy to replace old one, functionality automatically enabled
• Feature removed
• Miscellaneous: upgrade & downgrade compatibility, etc.

Checklist:

• I have added test cases for my bug fix or my new feature
• This pr needs user documentation (for new or modified features or behaviors)
  • I have added documentation for my new feature or new function

Bugfix cherry-pick branch check:

• I have checked the version labels which the pr will be auto-backported to the target branch
  • 3.2
  • 3.1
  • 3.0
  • 2.5

---

This is an automatic backport of pull request #35283 done by [Mergify](https://mergify.com). Why I'm doing: - The `SET_VAR` hint is only viable for query, but not DML

What I'm doing:

• Support set_var for insert/update/delete sql

Fixes #issue

What type of PR is this:

• BugFix
• Feature
• Enhancement
• Refactor
• UT
• Doc
• Tool

Does this PR entail a change in behavior?

• Yes, this PR will result in a change in behavior.
• No, this PR will not result in a change in behavior.

If yes, please specify the type of change:

• Interface/UI changes: syntax, type conversion, expression evaluation, display information
• Parameter changes: default values, similar parameters but with different default values
• Policy changes: use new policy to replace old one, functionality automatically enabled
• Feature removed
• Miscellaneous: upgrade & downgrade compatibility, etc.

Checklist:

• I have added test cases for my bug fix or my new feature
• This pr needs user documentation (for new or modified features or behaviors)
  • I have added documentation for my new feature or new function

[mergify]

Cherry-pick of cc2e5ad has failed:

On branch mergify/bp/branch-3.1/pr-35283
Your branch is up to date with 'origin/branch-3.1'.

You are currently cherry-picking commit cc2e5ad571.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   fe/fe-core/src/main/java/com/starrocks/sql/ast/DmlStmt.java
	new file:   fe/fe-core/src/test/java/com/starrocks/sql/plan/SetVarTest.java

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   fe/fe-core/src/main/java/com/starrocks/qe/StmtExecutor.java
	both modified:   fe/fe-core/src/main/java/com/starrocks/sql/parser/AstBuilder.java
	both modified:   fe/fe-core/src/main/java/com/starrocks/sql/parser/StarRocks.g4

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[mergify]

@mergify[bot]: Backport conflict, please reslove the conflict and resubmit the pr