Add FTP support to AbstractJobStore._get_size

[stxue1]

_get_size currently doesn't support FTP as it requires special commands and wizardry.

This will also need to support extracting username/password from the URL and/or supporting environmental variables to override the username/password

This will allow FTP files to work with #5133

┆Issue is synchronized with this Jira Story
┆Issue Number: TOIL-1660

[mr-c]

I implemented the equivalent of this in https://github.com/ohsu-comp-bio/cwl-tes/blob/03f0096f9fae8acd527687d3460a726e09190c3a/cwl_tes/ftp.py#L231
Feel free to steal!