[BugFix] support drop resource group if exists

[blanklin030]

Why I'm doing:

What I'm doing:

Fixes #45911

What type of PR is this:

• [ ] BugFix
• [ ] Feature
• [x] Enhancement
• [ ] Refactor
• [ ] UT
• [ ] Doc
• [ ] Tool

Does this PR entail a change in behavior?

• [x] 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
• [ ] This is a backport pr

Bugfix cherry-pick branch check:

• [x] I have checked the version labels which the pr will be auto-backported to the target branch
  • [x] 3.3
  • [x] 3.2
  • [x] 3.1
  • [x] 3.0
  • [x] 2.5

[CLAassistant]

All committers have signed the CLA.

[murphyatwork]

@blanklin030 can you sign the CLA ?

[murphyatwork]

@Mergifyio rebase

[mergify[bot]]

rebase

✅ Branch has been successfully rebased

[sonarqubecloud[bot]]

Quality Gate failed

Failed conditions
B Maintainability Rating on New Code (required ≥ A)

See analysis details on SonarCloud

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[github-actions[bot]]

[BE Incremental Coverage Report]

:white_check_mark: pass : 0 / 0 (0%)

[github-actions[bot]]

[FE Incremental Coverage Report]

:x: fail : 5 / 7 (71.43%)

file detail

	path	covered_line	new_line	coverage	not_covered_line_detail
:large_blue_circle:	com/starrocks/sql/ast/DropResourceGroupStmt.java	2	3	66.67%	[26]
:large_blue_circle:	com/starrocks/catalog/ResourceGroupMgr.java	3	4	75.00%	[428]