Bug: 4xx Salesforce pubsub errors not surfacing all error details

[samirketema]

Bug description

When a 4xx error is faced in the pubsub source, we are not surfacing the error details from the body. We ran into this recently when the connected app settings did not have the same authenticated user selected for the Client Credentials flow.

Steps to reproduce

1. Run the pubsub source against a Salesforce Connected App that does not have a user set for the Client Credentials Flow
2. Note that there is a 4xx error on OAuth, but it does not include details about the client credentials flow.
3. Run the same API call in curl / Postman, and note that the body contains useful error information, which is not surfaced by the connector

Version

pubsub branch