Set or unset a named value associated with a swif job.

Usage: tag-job -workflow W [-jid | -name] <job> -tag <tag-name> <tag-value>
Associate tag with job <job> having name <tag-name> and value <tag-value>.  A
job may have any number of tags, and multiple jobs can be assigned the same
tags if desired.

A tag is removed by specifying -untag <tag-name>.  You can specify multiple
-tag or -untag sets per invocation.

Example: Set tag t1=hello on job named "my-job-1" in workflow "my-wf".
swif tag-job my-wf -name my-job-1 -tag t1 hello

Example: Unset tag t1 on job with swif id 123 in workflow "my-wf".
swif tag-job my-wf -jid 123 -untag t1