Room event fields say content is the HTTP body

> When interacting with the REST API, this is the HTTP body.

This isn't entirely true if dealing with certain APIs. Should clarify what endpoints expect it to be the body rather than blanket statement this.

Review the room event field descriptions containing the statement that content is the HTTP body. Identify the affected wording and the endpoints where the statement is not accurate, then revise it to describe the applicable cases without making a blanket claim. Confirm that the resulting specification text distinguishes which endpoints expect content as the body.

Written by the indexing model from the issue text.