Add commands for interacting with Koji side-tag plugin
There is a Koji plugin that can create, list and remove side-tags [0].
This patch adds support for a commands to do that.
[0] https://pagure.io/sidetag-koji-plugin
It is used like this:
$ rpkg request-side-tag [--base-tag=FOO]
$ rpkg list-side-tags [--mine|--user=LOGIN] [--base-tag=FOO]
$ rpkg remove-side-tag TAG
The base tag is used as a parent of the new side tag. If not given, rpkg
will find build tag of current target and use it.
The plugin creates both tag and target (with the same name), so the
output of rpkg contains a suggestion on how to submit builds to the new
target.
Fixes: https://pagure.io/fedpkg/issue/329
JIRA: COMPOSE-3591
Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>