docs: add docs for content assignment list endpoint

[sameeramin]

Changes:

• added docs for content assignment list endpoint
• changed the order of the endpoints list to align with the numbering
• updated response item types

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• Subject matter expert: @sameenfatima78
• Subject matter expert: @zamanafzal
• Product review:
• Partner support:
• PM review: Mariana Hernandez Barroso

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Testing

• Ran ./run_tests.sh without warnings or errors

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