Provide a POST method for /wiki/rest/api/user/bulk

Issue Summary

Currently, the bulk get user endpoint only support GET method, where we need to provide the list of accountIDs as query parameters.

GET <site_url>/wiki/rest/api/user/bulk?accountId=<id1>&accountId=<id2>&accountId=<id3>.....

The downside of this is that when requesting large number of accountIds (documentation states that the endpoint support a max of 200 accountIds), the request header can exceed the maximum header size that's allowed. As a result, the request if rejected with a 400 Bad Request.

Please implement a POST method for this endpoint so that the accountIds can be put in the POST body instead. For example,

POST <site_url>/wiki/rest/api/user/bulk
Content-Type: application/json

{
	"accountIds": [
		"id1",
		"id2",
		"id3"
	]
}

Steps to Reproduce

1. make a large request with 200 accountIds with /wiki/rest/api/user/bulk

Expected Results

get a 200 OK response with results.

Actual Results

we get 400 Bad request.

Workaround

Only workaround is to reduce the number of accountIds per request. However, this method increases the total time required to fetch large dataset.