Add remove partner token section in the Connection Test page

[jorgemd24]

Changes proposed in this Pull Request:

This PR adds a section to revoke the WPCOM token associated with the Google client.

Screenshots:

Detailed test instructions:

1. Apply the WPCOM Diff D149792
2. Go to the Connection Test Page
3. Go to https://wordpress.com/me/security/connected-applications and check that you have your application connected there.
4. Click Revoke WPCOM Partner Access
5. Refresh https://wordpress.com/me/security/connected-applications and see that the connection is gone.
6. If there are not tokens associated you will get the following error {"code":"wpcom_partner_token_not_associated","message":"No token found associated with the client ID and user.","data":null}

Additional details:

Changelog entry

[puntope]

Looking good @jorgemd24 just please see my comment in th Diff D149792 regarding the endpoint structure

[jorgemd24]

Thanks @puntope for the review, I have updated the endpoint. This is ready for another round.

[puntope]

Thx @jorgemd24 LGTM ✅