feat: add query execution for mode discovery

[aaqilniz]

This PR and the related PRs at loopback-connector-mysql & loopback-datasource-juggler will enable cli's discoverer to add properties and their options based on the database's strict mode.

Checklist

• DCO (Developer Certificate of Origin) signed in all commits
• npm test passes on your machine
• New tests added or existing tests modified to cover all changes
• Code conforms with the style guide
• Commit messages are following our guidelines

[coveralls]

Pull Request Test Coverage Report for Build 8131673125

Details

• 1 of 8 (12.5%) changed or added relevant lines in 1 file are covered.
• 5 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.09%) to 59.222%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
lib/sql.js	1	8	12.5%

Files with Coverage Reduction	New Missed Lines	%
lib/sql.js	5	50.77%

Totals
Change from base Build 8101065918:	-0.09%
Covered Lines:	715
Relevant Lines:	1139

---

💛 - Coveralls