addFromURL to support pinning, through `pin: true` option

[tunnckoCore]

Probably most easier way is along these lines:

1. Change const sendOneFile = SendOneFile(moduleConfig(arg), 'add') to let

2. after the check of is valid url, add check for opts.pin === true and recreate sendOneFile

    if (!validUrl(url)) {
      return callback(new Error('"url" param must be an http(s) url'))
    }
    if (opts.pin === true) {
        sendOneFile = SendOneFile(moduleConfig(arg), 'pin/add')
    }
    
    requestWithRedirect(url, opts, sendOneFile, callback)

[lidel]

I am not sure what is your goal here, to automatically pin content added via addFromURL ?
AFAIK it calls ipfs.add which pins by default already:

ipfs add --help | grep Pin
  --pin                              bool   - Pin this object when adding. Default: true.

[tunnckoCore]

Hm. Didn't know that.