Manage user sessions documentation page unclear

**Describe the content issue**:
Can you please expand this documentation to list at least the following things:
- When is the backend actually called both for getCurrentUser and fetchAuthSession or does the information just come from locally stored tokens?
- What do both the getCurrentUser and fetchAuthSession functions do in the following cases:
- User credentials are present but have expired
- User credentials are not present

What also would help greatly is a link to a general reference somewhere which seems to be completely absent from these docs. It is a massive pain to implement this at the moment and involves lots of trial and error and looking at the browser console. I feel that including this bare minimum information would already help a lot.

Also, where is the general reference to all methods? I understand that many pre-cooked fronend components and UIs are added in the new amplify library but this cannot be a replacement for actually documenting the amplify frontend library somewhere IMO. If it's there it is extremely hard to find.

**URL page where content issue is**:
https://docs.amplify.aws/vue/build-a-backend/auth/connect-your-frontend/manage-user-sessions/

Start by reviewing the Vue manage-user-sessions page at the URL in the issue and trace the existing references for getCurrentUser and fetchAuthSession. Done means documenting backend calls and behavior for expired or missing credentials, and adding a discoverable link to a complete frontend method reference.

Written by the indexing model from the issue text.