Add callout, Auth event channel changes with Hub in v6

**Describe the content issue**:
A clear and concise description of what the content issue is. Is there content missing or is there incorrect content?

As detailed in `amplify-js` issue [#12681](https://github.com/aws-amplify/amplify-js/issues/12681), there is no callout or warning when upgrading from v5 to v6 for the changes to the Hub events emitted in the Auth channel. Any logic built upon the v5 events that are no longer emitted could potentially break functionality when upgrading to v6.

**URL page where content issue is**:

[v5 Auth Events](https://docs.amplify.aws/react/prev/build-a-backend/auth/auth-events/#listen-to-and-log-auth-events)

vs.

[v6 Auth Events ](https://docs.amplify.aws/react/build-a-backend/auth/auth-events/#listen-to-and-log-auth-events)