Today, we disable CORS by default, but if a user simply enables CORS their instance of
elasticsearch will allow cross origin requests from anywhere, as the default value for allowed
origins is `*`.
This changes the default to be `null` so that no origins are allowed and the user must explicitly
specify the origins they wish to allow requests from. The documentation also mentions that there
is a security risk in using `*` as the value.
Closes#11169
6b086dc7db