docs: add documentation for license assign and bulk-revoke endpoints

[sameenfatima78]

Add a description of your changes with links to any relevant material. JIRA: https://2u-internal.atlassian.net/browse/ENT-7997

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Reviewers

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• [x] Subject matter expert: @zamanafzal
• [ ] Subject matter expert: @hamzawaleed01
• [ ] Product review: Mariana Hernandez Barroso
• [ ] Partner support:
• [ ] PM review:

FYI: Tag anyone else who might be interested in this PR here.

Testing

• [x] Ran ./run_tests.sh without warnings or errors

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