Send token in Authorization header from SDK requests

[3mcd]

This PR adds a new auth method to the SDK which takes an instance ID and auth token and fetches user details from core. The other SDK methods were also updated to pass the token to their respective API endpoints using the Authorization header.

Issue(s) Resolved

N/A

Test Plan

1. Log into core and visit the Unjournal community.
2. Go to http://localhost:3000/c/unjournal/stages (or https://core-pr-74-y0x1.onrender.com/c/unjournal/stages if testing through review app).
3. Click on the first pub's integrations dropdown button ("6 integrations") and click "Submit Pub"
4. In the browser's search bar replace https://integration-submissions.onrender.com with http://localhost:3002 (or https://integration-submissions-pr-74.onrender.com if testing through review app).
5. You should see "Hello, Jill Admin" along with the user's avatar.

[kalilsn]

approved by jill admin