fix: disable cors by default (#3275)

Co-authored-by: Marcin Rataj <[email protected]>

Brings js-ipfs into line with go-ipfs by not having CORS on by default, instead requiring the user to explicitly configure it.

BREAKING CHANGE:

- CORS origins will need to be [configured manually](https://github.com/ipfs/js-ipfs/blob/master/packages/ipfs-http-client/README.md#cors) before use with ipfs-http-client

Author: achingbrain

README.md

@@ -342,6 +342,8 @@ $ ipfs config --json API.HTTPHeaders.Access-Control-Allow-Origin  '["http://exam
 $ ipfs config --json API.HTTPHeaders.Access-Control-Allow-Methods '["PUT", "POST", "GET"]'
 ```
 
+If you are using `js-ipfs`, substitute `ipfs` for `jsipfs` in the commands above.
+
 ### Custom Headers
 
 If you wish to send custom headers with each request made by this library, for example, the Authorization header. You can use the config to do so: