60895 Add batch support to users REST API WP_REST_Users_Controller

[alexminza]

Following the development discussions in #53063 and #50244 for some reason batch support was not added to users.

We were working on importing a large number of users as part of a migration project to WordPress / WooCommerce to discover that WP REST API does not support batching for Users in WP_REST_Users_Controller since allow_batch is not explicitly set to true in register_rest_route.

This PR adds batch support for users in WP_REST_Users_Controller.

Example batch create users request:

curl --location 'http://localhost:8080/wp-json/batch/v1' \
--header 'Content-Type: application/json' \
--header 'Authorization: Basic ##REDACTED##' \
--data-raw '{
    "requests": [
        {
            "method": "POST",
            "path": "/wp/v2/users",
            "body": {
                "username": "testuser1",
                "email": "testuser1@localhost.local",
                "password": "##REDACTED##"
            }
        },
        {
            "method": "POST",
            "path": "/wp/v2/users",
            "body": {
                "username": "testuser2",
                "email": "testuser2@localhost.local",
                "password": "##REDACTED##"
            }
        }
    ]
}'

Trac ticket: https://core.trac.wordpress.org/ticket/60895
Reference: https://core.trac.wordpress.org/ticket/53063

---

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[github-actions]

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[github-actions]

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[alexminza]

@TimothyBJacobs you added the main support for batching https://core.trac.wordpress.org/ticket/53063 - what do you think about this change?