Move internal-ghorgs to salesforce and drop orgs.yaml

[kdmccormick]

This is follow-up from the work done in #207, which allowed us to delete people.yaml

The only thing we still use the manually-maintained orgs.yaml file for is the internal-ghorgs settings, which tells the OSPR bot that it can bypass automated triage process for certain "internal" entities like Axim, 2U, and Arbisoft.

If we were able to move this setting into Salesforce and pull it down from salesforce-export.csv, it would make it so all our OSPR data is is a single, auto-updating file.

Furthermore, if we can use Salesforce to validate the data, then we no longer need to run unit tests on https://github.com/openedx/openedx-webhooks-data just to validate the consistency of the data files.

Value:

• Simpler for Axim on-call to understand how this all works
• Less openedx-webhooks code to maintain
• Less potential for confusion around outdated data in orgs.yaml
• Potentially able to archive https://github.com/openedx/openedx-webhooks-data-schema/ and remove the unit tests from https://github.com/openedx/openedx-webhooks-data