QnAMaker - Add getAnswers(), fix options in constructor, add metadata, create queryQnaMakerService()

[Zerryth]

Fixes #637, #551, #675, microsoft/botframework-sdk#5143

Specific Changes

• Added strictFilters and metadataBoost in QnAMakerOptions interface
• Created QnAMakerMetadata interface for strictFilters and metadataBoost and parity with C#
• QnAMaker class constructor now assignsoptions argument passed in to _options property and doesn't only keep hard-coded defaults
• deprecated generateAnswers()
• created new getAnswers() to accept QnAMakerOptions and emit trace
• created queryQnaService() which also accepts QnAMakerOptions
• callService() now calls new queryQnaService()
• changed to use async/await syntax
• added User-Agent header to requests to QnAMaker service
• removed link to sample 11. qnamaker, as it uses method generateAnswer() that this PR will deprecate

To-Do: write more tests

[coveralls]

Pull Request Test Coverage Report for Build 2385

• 44 of 49 (89.8%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.04%) to 82.285%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
libraries/botbuilder-ai/src/qnaMaker.ts	44	49	89.8%

Files with Coverage Reduction	New Missed Lines	%
libraries/botbuilder-ai/src/qnaMaker.ts	1	88.17%

Totals
Change from base Build 2375:	0.04%
Covered Lines:	2663
Relevant Lines:	3115

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💛 - Coveralls