Add requisition list to the supported REST import types

[keharper]

Purpose of this pull request

Adds requisition_list as a supported entity type for the REST Import API (Adobe Commerce SaaS editions only) and simplifies the endpoint URL format used throughout the page.

Key changes:

• Adds requisition_list to the list of supported import entity types, tagged as SaaS-only.
• Updates parameter tables for both the CSV and JSON import endpoints to include requisition_list, noting that append, replace, and delete behaviors are supported.
• Adds a new Requisition list payload section under the JSON Import API, with a field reference table and a JSON example that creates two requisition lists.
• Adds a Store: <store code> header note for SaaS to the JSON endpoint.
• Simplifies endpoint URLs throughout the page from POST /rest/<store_view_code>/V1/import/* to POST /V1/import/* for consistency with current API conventions.
• Minor editorial fixes: corrects heading capitalization ("Customers and addresses") and renames "Payload 7 (Multiple select attributes)" to "Multiple select attributes payload".

Affected pages

• https://developer.adobe.com/commerce/webapi/rest/modules/import

Links to Magento Open Source code

N/A