[SQL Migration] Fix schema migration table selection issue

[siyao-Siyang]

Issue:
If tables in "Missing on target" tab are selected, schema migration option won't be checked automatically. It causes that the selected tables dont exist in target and fail the SqlInfoCollector validation.

Fix:
if users don't select schema migration option and just select the tables in "missing on target" tab, enable schema migration automatically.

[coveralls]

Pull Request Test Coverage Report for Build 7228187689

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.001%) to 41.603%

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Files with Coverage Reduction	New Missed Lines	%
src/sql/workbench/services/connection/browser/connectionDialogWidget.ts	1	73.44%

Totals
Change from base Build 7191361300:	-0.001%
Covered Lines:	30817
Relevant Lines:	69389

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💛 - Coveralls