Add sample for user ID and more validation logics

[compulim]

Background

If user ID is not specified, default will be default-user.

Although conversation is identified/partitioned by conversation ID, user state use user ID. That means, multiple conversations with same user ID will share same user state.

In README.md, we didn't spec out how to specify userID. This PR will add the documentation and more checks to make sure the userID passed is okay:

• userID can be specified by props or embedded in Direct Line token.
  • If the userID is both specified and embedded, we prefer the embedded one from Direct Line token.
• userID must be a string.
• userID passed from props cannot prefix with dl_.
  • Embedded user ID is always prefixed with dl_, and this user ID is "forgery-proof". This checks reduces the confusion between a forgery-proof user ID and a non-forgery-proof one.

Changelog

Added

• Fix #1344, by updating README.md and adding validation logic for userID props, in #1447
  • If userID props present and also embedded in Direct Line token, will use the one from Direct Line token
  • If userID props present, they must be string and not prefixed with dl_, to avoid confusion between userID props and Direct Line embedded user ID (which is forgery-proof)
  • If userID props does not pass the validation test or not specified, Web Chat will use default-user instead

[tonyanziano]

👍

[coveralls]

Pull Request Test Coverage Report for Build 557

• 0 of 7 (0.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.2%) to 44.82%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
packages/core/src/sagas/connectSaga.js	0	7	0.0%

Totals
Change from base Build 547:	-0.2%
Covered Lines:	713
Relevant Lines:	1418

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💛 - Coveralls