[SE-5068] refactor: use openedx GitHub org instead of edx
Description
This PR replaces the edx GitHub org in the configuration and hardcoded URLs with openedx reflecting the organizational changes done recently.
Supporting information
As part of the task, the P&T and other client instancess will need to be redeployed manually.
Dependencies
N/A
Screenshots
Sandbox
Testing instructions
Do a basic instance [checklist|https://handbook.opencraft.com/en/latest/processes/instance_checklist/]
Deadline
N/A