Dev/brih/feature/public preview sql db

[brian-harris]

This PR contains final updates for SQL DB public preview:

• updates database backup page name to more general description
• add PREVIEW text to SQL DB migration text
• bump version to 1.0.6 for next release
• fix bug to update source / target table mapping UX
• fix bug to prevent invalid username or password being edited and passed onto the migration
• update readme to include SQL DB migration scenario

[coveralls]

Pull Request Test Coverage Report for Build 3102695791

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 4 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.01%) to 42.442%

---

Files with Coverage Reduction	New Missed Lines	%
extensions/notebook/src/jupyter/serverInstance.ts	4	75.5%
<!--	Total:	4

Totals
Change from base Build 3101583077:	-0.01%
Covered Lines:	29239
Relevant Lines:	64081

---

💛 - Coveralls