Bot-docs: Add Teams Manifest Guidance to v4 docs

[emgrol]

In issue #1294 @iMicknl noted that the following information about authentication and Teams that's currently in the v3 docs is missing from the v4 docs:

The manifest is missing token.botframework.com as an entry in the validDomains section, which is required by the Teams channel. If this is missing, the user won't see an error, pressing the Sign In card button will do nothing at all.

@iMicknl suggested we add the following note in from this article somewhere in the v4 docs as well:

Adding a bot by GUID, for anything other than testing purposes, is not recommended. Doing so severely limits the functionality of a bot. Bots in production use should be added to Teams as part of an app. See Create a bot and Test and debug your Microsoft Teams bot

[mmiele]

Work in progress.
See PR: https://github.com/MicrosoftDocs/bot-docs-pr/pull/1685.

[mmiele]

@iMicknl The documents have been updated based on your suggestions. The related PR is: https://github.com/MicrosoftDocs/bot-docs-pr/pull/1685.
Please, review the following staged documents:
1) Manifest. https://review.docs.microsoft.com/en-us/azure/bot-service/bot-builder-authentication?view=azure-bot-service-4.0&branch=pr-en-us-1685&tabs=csharp%2Cbot-oauth
2) GUID. https://review.docs.microsoft.com/en-us/azure/bot-service/channel-connect-teams?view=azure-bot-service-3.0&branch=pr-en-us-1685

[iMicknl]

@mmiele looks good, thanks!

[mmiele]

Updated docs available in the next doc build. Thanks.