rename url in pin remote to endpoint

[Gozala]

Per @lidel we use endpoint option everywhere in ipfs-client, but then e.g. if user omits endpoint option go-ipfs will produce error with message "argument "url" is required", which can be very confusing for the user.

We should either change naming in go-ipfs as well from url to endpoint everywhere, or change it back to url in js-ipfs.

[lidel]

I believe this will be addressed by #7823 where we switched to "endpoint" everywhere