adding jest.enable setting and adjust workspace operations accordingly

[connectdotz]

Adding a new setting jest.enable to completely turn the extension off for a given workspace. Also, incorporate this in the monorepo setup tool so we will ignore the disabled workspace.

Note

1. this indeed overlaps with the "disabledWorkspaceFolders" setting, albeit served different use cases.
2. I wasn't sure if we really needed this feature since the user could simply use the vscode feature to disable the extension for the specific workspace. But it might be useful for the monorepo use cases, where you just want to disable a specific folder rather than the whole workspace. So go ahead added it to close the requirement.

resolve #984
resolve #981
resolve #993

[coveralls]

Pull Request Test Coverage Report for Build 4152419526

• 43 of 43 (100.0%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.03%) to 97.751%

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Totals
Change from base Build 4108646033:	0.03%
Covered Lines:	3407
Relevant Lines:	3430

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💛 - Coveralls