Use @adobe/auth-token beta. Fix tests. Switch to jest.

[brenthosie]

Description

Supports the new oauth-server-to-server credential Type. Drops support for JWT credentials.

Closes #63 .

Related Issue

https://jira.corp.adobe.com/browse/PDCL-11570

Motivation and Context

How Has This Been Tested?

1. Manual testing
2. Automated tests

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[h-singhal]

When we are trying to use v6.0.0-beta.11 or v6.0.0-beta.12 or v6.0.0-beta.13...
we are getting below Error :

Any update to support the oauth-server-to-server credential Type

[brenthosie]

Closes #70