[auth][github]: add automatic auth flow to obtain a GitHub token

[legomushroom]

When adding a GitHub connector, we ask user for the GitHub PAT to get information about their repo/issues:

Currently, there is no way to get that token for the end-user thought. We need to add an authentication flow that will generate GitHub PAT and pass it into the Togezr extension. We can use an Azure Function for the redirection service:

1. Add the "Please sign in" notification instead of the input.
2. The GitHub app will redirect to an Azure function endpoint which will exchange the authorization code to the access token.
3. The Azure function then should redirect to the vscode protocol handler continue the command flow.

Plan:

• Implement the Azure function.
• Implement the protocol handler for the extension.
• Implement the "wait on auth" provider that can be cancelled by the user.

Live Share:

⎇ legomushroom/github-oauth [ ⇄ master ]

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[legomushroom]

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