refactor: remove EdX-Api-Key usage

[mudassir-hafeez]

What are the relevant tickets?

#2872

Description (What does it do?)

This PR removes EDX_API_KEY usage as Open edX is going to remove the EDX_API_KEY. Details can be found at openedx/edx-platform#34039.

Screenshots (if appropriate):

• Desktop screenshots
• Mobile width screenshots

How can this be tested?

• Fetch and check out to this branch, and check that edX is configured properly.
• Test all the endpoints that currently utilize EdX-Api-Key for client requests, or follow the testing instructions mentioned in refactor: remove X-EdX-Api-Key usage edx-api-client#104. It's important to thoroughly test all the instructions provided in this PR.

Additional Context

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[asadali145]

LGTM! We need to merge mitodl/edx-api-client#104 and release the edx-api-client and then update this xPro PR with the new version of edx-api-client.

[asadali145]

@mudassir-hafeez there is conflict. Could you resolve?

[mudassir-hafeez]

@asadali145 can you please re-review as the conflict is resolved? also bumped edx-api-client version to 1.9.0 as it was published to PYPI.

[asadali145]

LGTM!